3. Property and Equipment, net, and Other Assets

At September 30, 2018 and December 31, 2017, property and equipment, net, and other assets consisted of the following:

	September 30,		December 31,
	2018		2017
	(Unaudited)
Property and equipment, net of accumulated depreciation of $2,446,746 and $2,193,231 as of September 30, 2018 and December 31, 2017, respectively	$	698,587	$	956,867
Security deposits and other assets		345,192		363,475
Property and equipment, net, and other assets	$	1,043,779	$	1,320,342

We compute depreciation using the straight-line method over the estimated useful lives of the property and equipment. Depreciation expense for the three months ended September 30, 2018 was $97,679, including $45,576 of depreciation expense reflected within “Cost of revenue” in our condensed consolidated statements of operations as it related to assets used in directly servicing customer contracts, and was $301,651 for the nine months ended September 30, 2018, including $136,574 of depreciation expense reflected within “Cost of revenue.” Depreciation expense for the three months ended September 30, 2017 was $110,582, including $43,462 of depreciation expense reflected within “Cost of revenue,” and was $339,272 for the nine months ended September 30, 2017, including $126,761 of depreciation expense reflected within “Cost of revenue.” At September 30, 2018, the carrying value of our capital lease assets was $165,630, net of $334,467 of accumulated depreciation. At December 31, 2017, the carrying value of our capital lease assets was $243,778, net of $256,319 of accumulated depreciation.

On February 20, 2018 (the “Closing Date”), we entered into an Asset Purchase Agreement with Earth Media Partners, LLC to sell certain assets of our wholly owned subsidiary, Earth911, Inc., in exchange for a 19% interest in Earth Media Partners, LLC, which was recorded as an investment in the amount of $246,585 as of the Closing Date, and a potential future earn-out amount of approximately $350,000. The net assets sold related to the Earth911.com website business and consisted primarily of the website and its content and customers, deferred revenues, and accounts receivable as of the Closing Date. Following the Closing Date, Earth911, Inc. was subsequently renamed Quest Sustainability Services, Inc. In addition to our investment in Earth Media Partners, LLC, we accrued a receivable in the amount of $39,521 related to the earn-out as of September 30, 2018. The carrying amount of our investment and the accrued earn-out receivable are included in other assets.