At December 31, 2019 and 2018, Property and equipment, net, and other assets consisted of the following:

	As of December 31,
	2019			2018
Vehicles	$	493,373		$	493,373
Computer equipment		247,776			700,218
Office furniture and fixtures		541,464			541,464
Machinery and equipment		688,137			845,128
Leasehold improvements		558,035			558,035
Property and equipment, gross		2,528,785			3,138,218
Accumulated depreciation		(1,994,320	)		(2,523,700	)
Property and equipment, net		534,465			614,518
Right-of-use operating lease asset		1,595,044			—
Security deposits and other assets		306,585			353,507
Property and equipment, net, and other assets	$	2,436,094		$	968,025

We compute depreciation using the straight-line method over the estimated useful lives of the property and equipment. Depreciation expense for the year ended December 31, 2019 was $225,061, including $87,053 of depreciation expense reflected within “Cost of revenue” in our consolidated statement of operations as it related to assets used directly in servicing customer contracts. Depreciation expense for the year ended December 31, 2018 was $385,863, including $184,404 depreciation expense recorded in “Cost of revenue.”

We recorded a right-of-use operating lease asset of $2.0 million related to our corporate office lease upon the adoption of ASC 842 effective January 1, 2019. Refer to Note 7, Leases for additional information.

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. Earth911, Inc. was subsequently renamed Quest Sustainability Services, Inc. The carrying amount of our investment in Earth Media Partners, LLC is included in “Security deposits and other assets” and we have an accrued receivable in the amount of $163,781 related to the earn-out included in “Accounts receivable” as of December 31, 2019.