Estimating Useful Life and Percent Used Up The property and equipment footnote from Tesla follows. 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): 2018 2017 December 31 Machinery, equipment, vehicles and office furniture Tooling Leaseholder improvements Land and buildings Computer equipment, hardware and software Construction in progress $6,328,966 $4,251,711 1,397,514 1,255,952 960,971 789,751 4,047,006 2,517,247 487,421 395,067 807,297 2,541,588 14,029,175 11,751,316 (2,699,098) (1,723,794) $11,330,077 $10,027,522 Less accumulated depreciation Total *Weighted 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. X 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%) X %