SIGNATURES

Dated: March 14, 2019

SOTER CAPITAL, LLC

By:	/s/ Mary Ann Sigler
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Name:  Mary Ann Sigler
Title:  President and Treasurer

SOTER CAPITAL HOLDINGS, LLC

By:	/s/ Mary Ann Sigler
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Name:  Mary Ann Sigler
Title:  President and Treasurer

PE SOTER HOLDINGS, LLC

By:	/s/ Mary Ann Sigler
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Name:  Mary Ann Sigler
Title:  President and Treasurer

PLATINUM EQUITY CAPITAL SOTER PARTNERS, L.P.
By:  Platinum Equity Partners III, LLC, its general partner
By:  Platinum Equity Investment Holdings III, LLC, its senior managing member

By:	/s/ Mary Ann Sigler
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Name:  Mary Ann Sigler
Title:  Vice President and Treasurer

PLATINUM EQUITY PARTNERS III, LLC
By:  Platinum Equity Investment Holdings III, LLC, its senior managing member

By:	/s/ Mary Ann Sigler
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Name:  Mary Ann Sigler
Title:  Vice President and Treasurer

PLATINUM EQUITY INVESTMENT HOLDINGS III, LLC

By:	/s/ Mary Ann Sigler
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Name:  Mary Ann Sigler
Title:  Vice President and Treasurer

PLATINUM EQUITY INVESTCO, L.P.
By: Platinum Equity Investment Holdings IC (Cayman), LLC, its general partner

By:	/s/ Mary Ann Sigler
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Name:  Mary Ann Sigler
Title:  President

PLATINUM EQUITY INVESTMENT HOLDINGS IC (CAYMAN), LLC

By:	/s/ Mary Ann Sigler
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Name:  Mary Ann Sigler
Title:  President

PLATINUM INVESTCO (CAYMAN), LLC

By:	/s/ Mary Ann Sigler
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Name:  Mary Ann Sigler
Title:  President

PLATINUM EQUITY INVESTMENT HOLDINGS, LLC

By:	/s/ Mary Ann Sigler
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Name:  Mary Ann Sigler
Title:  Vice President and Treasurer

PLATINUM EQUITY INVESTMENT HOLDINGS III MANAGER, LLC

By:	/s/ Mary Ann Sigler
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Name:  Mary Ann Sigler
Title:  President


PLATINUM EQUITY, LLC

By: 	/s/ Mary Ann Sigler
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Name:  Mary Ann Sigler
Title:  Executive Vice President, Chief Financial Officer and Treasurer

Tom Gores

/s/ Mary Ann Sigler
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Mary Ann Sigler
Attorney-in-Fact



[Signature Page to Form 4]