<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><Version>2.4.0.8</Version><ReportLongName>00000013 - Disclosure - 8. Lines of Credit</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column FlagID="0"><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><CurrencyCode /><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName /><CurrencySymbol /><contextRef><ContextID>from-2013-01-01-to-2013-06-30.12129.0.0.0.0.0.0.0</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0001335239</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2013-01-01T00:00:00</PeriodStartDate><PeriodEndDate>2013-06-30T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS /><CurrencyCode /><OriginalCurrencyCode /></MCU><CurrencySymbol /><Labels><Label Key="CalendarSupplement" Id="0" Label="6 Months Ended" /><Label Key="Calendar" Id="1" Label="Jun. 30, 2013" /></Labels></Column></Columns><Rows><Row FlagID="0"><Id>1</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>1</Level><ElementName>us-gaap_LineOfCreditFacilityAbstract</ElementName><ElementPrefix>us-gaap_</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>Line of Credit Facility [Abstract]</Label></Row><Row FlagID="0"><Id>2</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>2</Level><ElementName>epaz_LineOfCreditFacilityDisclosureTextBlock</ElementName><ElementPrefix>epaz_</ElementPrefix><IsBaseElement>false</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="from-2013-01-01-to-2013-06-30.12129.0.0.0.0.0.0.0" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;&lt;b&gt;Note 8 &amp;#150; Lines of Credit&lt;/b&gt;&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify"&gt;Lines of credit consisted of the following at
June 30, 2013 and December 31, 2012, respectively:&lt;/p&gt;

&lt;p style="font: 8pt Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;

&lt;table cellspacing="0" cellpadding="0" style="font: 8pt Times New Roman, Times, Serif; width: 100%; border-collapse: collapse"&gt;
&lt;tr style="vertical-align: bottom"&gt;
    &lt;td style="text-align: justify"&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td colspan="2" style="text-align: center"&gt;&lt;font style="font-size: 8pt"&gt;June 30,&lt;/font&gt;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td colspan="2" style="text-align: center"&gt;&lt;font style="font-size: 8pt"&gt;December 31,&lt;/font&gt;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;
&lt;tr style="vertical-align: bottom"&gt;
    &lt;td style="text-align: justify"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="padding-bottom: 1pt"&gt;&amp;#160;&lt;/td&gt;
    &lt;td colspan="2" style="border-bottom: black 1pt solid; text-align: center"&gt;&lt;font style="font-size: 8pt"&gt;2013&lt;/font&gt;&lt;/td&gt;
    &lt;td style="padding-bottom: 1pt"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="padding-bottom: 1pt"&gt;&amp;#160;&lt;/td&gt;
    &lt;td colspan="2" style="border-bottom: black 1pt solid; text-align: center"&gt;&lt;font style="font-size: 8pt"&gt;2012&lt;/font&gt;&lt;/td&gt;
    &lt;td style="padding-bottom: 1pt"&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;
&lt;tr style="vertical-align: bottom; background-color: #CCFFCC"&gt;
    &lt;td style="width: 74%; text-align: justify"&gt;&lt;font style="font-size: 8pt"&gt;Line of credit of $50,000 from PNC bank, originating on February 16, 2012. The outstanding balance on the line of credit bears interest at an introductory rate of 4.25% for the first year, subject to renewal thereafter. Payments of $739 are due monthly.&lt;/font&gt;&lt;/td&gt;
    &lt;td style="width: 1%"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="width: 1%"&gt;&lt;font style="font-size: 8pt"&gt;$&lt;/font&gt;&lt;/td&gt;
    &lt;td style="width: 10%; text-align: right"&gt;&lt;font style="font-size: 8pt"&gt;49,947&lt;/font&gt;&lt;/td&gt;
    &lt;td style="width: 1%"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="width: 1%"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="width: 1%"&gt;&lt;font style="font-size: 8pt"&gt;$&lt;/font&gt;&lt;/td&gt;
    &lt;td style="width: 10%; text-align: right"&gt;&lt;font style="font-size: 8pt"&gt;49,606&lt;/font&gt;&lt;/td&gt;
    &lt;td style="width: 1%"&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;
&lt;tr style="vertical-align: bottom; background-color: white"&gt;
    &lt;td style="text-align: justify"&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="text-align: right"&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="text-align: right"&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;
&lt;tr style="vertical-align: bottom; background-color: #CCFFCC"&gt;
    &lt;td style="text-align: justify"&gt;&lt;font style="font-size: 8pt"&gt;Line of credit of $20,000 from US Bank, originating on June 8, 2012. The outstanding balance on the line of credit bears interest at 9.75%, maturing on June 5, 2019. Payments of $500 are due monthly.&lt;/font&gt;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="text-align: right"&gt;&lt;font style="font-size: 8pt"&gt;19,673&lt;/font&gt;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="text-align: right"&gt;&lt;font style="font-size: 8pt"&gt;19,641&lt;/font&gt;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;
&lt;tr style="vertical-align: bottom; background-color: white"&gt;
    &lt;td style="text-align: justify"&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="text-align: right"&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="text-align: right"&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;
&lt;tr style="vertical-align: bottom; background-color: #CCFFCC"&gt;
    &lt;td style="padding-bottom: 1pt; text-align: justify"&gt;&lt;font style="font-size: 8pt"&gt;Line of credit of $40,000 from Dell Business Credit available for the purchase of Dell products, such as computer and software equipment. The outstanding balance on the line of credit bears interest at a rate of 26.99%. Variable payments are due monthly.&lt;/font&gt;&lt;/td&gt;
    &lt;td style="padding-bottom: 1pt"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="border-bottom: black 1pt solid"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="border-bottom: black 1pt solid; text-align: right"&gt;&lt;font style="font-size: 8pt"&gt;5,317&lt;/font&gt;&lt;/td&gt;
    &lt;td style="padding-bottom: 1pt"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="padding-bottom: 1pt"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="border-bottom: black 1pt solid"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="border-bottom: black 1pt solid; text-align: right"&gt;&lt;font style="font-size: 8pt"&gt;7,800&lt;/font&gt;&lt;/td&gt;
    &lt;td style="padding-bottom: 1pt"&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;
&lt;tr style="vertical-align: bottom; background-color: white"&gt;
    &lt;td style="text-align: justify"&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="text-align: right"&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="text-align: right"&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;
&lt;tr style="vertical-align: bottom; background-color: #CCFFCC"&gt;
    &lt;td style="text-align: justify"&gt;&lt;font style="font-size: 8pt"&gt;Total line of credit&lt;/font&gt;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="text-align: right"&gt;&lt;font style="font-size: 8pt"&gt;74,937&lt;/font&gt;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="text-align: right"&gt;&lt;font style="font-size: 8pt"&gt;77,047&lt;/font&gt;&lt;/td&gt;
    &lt;td&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;
&lt;tr style="vertical-align: bottom; background-color: white"&gt;
    &lt;td style="padding-bottom: 1pt; text-align: justify"&gt;&lt;font style="font-size: 8pt"&gt;Less: current portion&lt;/font&gt;&lt;/td&gt;
    &lt;td style="padding-bottom: 1pt"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="border-bottom: black 1pt solid"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="border-bottom: black 1pt solid; text-align: right"&gt;&lt;font style="font-size: 8pt"&gt;(74,937&lt;/font&gt;&lt;/td&gt;
    &lt;td style="padding-bottom: 1pt"&gt;&lt;font style="font-size: 8pt"&gt;)&lt;/font&gt;&lt;/td&gt;
    &lt;td style="padding-bottom: 1pt"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="border-bottom: black 1pt solid"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="border-bottom: black 1pt solid; text-align: right"&gt;&lt;font style="font-size: 8pt"&gt;(77,047&lt;/font&gt;&lt;/td&gt;
    &lt;td style="padding-bottom: 1pt"&gt;&lt;font style="font-size: 8pt"&gt;)&lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr style="vertical-align: bottom; background-color: #CCFFCC"&gt;
    &lt;td style="padding-bottom: 2.5pt; text-align: justify"&gt;&lt;font style="font-size: 8pt"&gt;Line of credit, less current portion&lt;/font&gt;&lt;/td&gt;
    &lt;td style="padding-bottom: 2.5pt"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="border-bottom: black 2.25pt double"&gt;&lt;font style="font-size: 8pt"&gt;$&lt;/font&gt;&lt;/td&gt;
    &lt;td style="border-bottom: black 2.25pt double; text-align: right"&gt;&lt;font style="font-size: 8pt"&gt;&amp;#150;&lt;/font&gt;&lt;/td&gt;
    &lt;td style="padding-bottom: 2.5pt"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="padding-bottom: 2.5pt"&gt;&amp;#160;&lt;/td&gt;
    &lt;td style="border-bottom: black 2.25pt double"&gt;&lt;font style="font-size: 8pt"&gt;$&lt;/font&gt;&lt;/td&gt;
    &lt;td style="border-bottom: black 2.25pt double; text-align: right"&gt;&lt;font style="font-size: 8pt"&gt;&amp;#150;&lt;/font&gt;&lt;/td&gt;
    &lt;td style="padding-bottom: 2.5pt"&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;
&lt;/table&gt;</NonNumbericText><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>nonnum:textBlockItemType</ElementDataType><SimpleDataType>na</SimpleDataType><ElementDefenition>Line of credit discussion</ElementDefenition><ElementReferences>No definition available.</ElementReferences><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>Line of Credit</Label></Row></Rows><Footnotes /><IsEquityReport>false</IsEquityReport><ReportName>8. Lines of Credit</ReportName><MonetaryRoundingLevel>UnKnown</MonetaryRoundingLevel><SharesRoundingLevel>UnKnown</SharesRoundingLevel><PerShareRoundingLevel>UnKnown</PerShareRoundingLevel><ExchangeRateRoundingLevel>UnKnown</ExchangeRateRoundingLevel><HasCustomUnits>true</HasCustomUnits><IsEmbedReport>false</IsEmbedReport><IsMultiCurrency>false</IsMultiCurrency><ReportType>Sheet</ReportType><RoleURI>http://epazz.com/role/LineOfCredit</RoleURI><NumberOfCols>1</NumberOfCols><NumberOfRows>2</NumberOfRows></InstanceReport>
