When originally purchased, a vehicle costing $23,000 had an estimated useful life of 8 years and an estimated salvage value of $3,000. after 4 years of straight-line depreciation, the asset's total estimated useful life was revised from 8 years to 6 years and there was no change in the estimated salvage value. the depreciation expense in year 5 equals:?

For the initial case: the annual straight-line depreciation would be (23,000 - 3,000) / 8 = $2,500/yr. After 4 years, the value would be lower by $2500*4 = $10000, so 23,000 - 10,000 = $13,000 book value.
Revising the estimated life down to 6 years means that only 2 years remain, so the new straight-line depreciation is (13,000 - 3,000) / 2 = $5,000/yr
Therefore, the depreciation expense in year 5 is $5,000.