The property and equipment footnote from Tesla foliows. Assume that 25% of the amount classified as "Land and buildings" pertains to the cost of the Land. Property and Depreciation Our property, plant and equipment, net, consists of the following (in thousands): December 31 2018 2017 Machinery, equipment, vehicles and offce furniture $6,328,965 54,251,711 Tooling Leaseholder improvements Land and huildings 1,397,514 1,255,952 960,971 789,751 4,047,006 2,517,247 Computer equipment, hardware and software 487,421 395,067 Construction in progress 807,297 2,541,588 14,029,175 11,751,316 Less accurmulated depreciation (2,699,098) (1,723,794) Total $11,330,077 $10,027,522 wWeighted averages Depreciation expense during the years ended December 31, 2018, 2017, and 2016 was $1.11 billion, $769.3 million, and $477.3 million, respectively. a. Compute the average useful life of Tesla's depreciable assets at year-end 2018, Round answer to one decimal place. years b. Estimate the percent used up of Tesla's depreciable assets at year-end 2018. Round answer to one decimal place (ex: 0.2345 = 23.5%)