Revision of Depreciation A building with a cost of $8 a. What is the amount of the annual depreciation? 10,000 has an estimated residual value of $162,000, has an estimated useful life of 36 years, and is depreciated by the straight-line method b. What is the book value at the end of the twentieth year of use? c. If at the start of the twenty-first year it is estimated that the remaining ife is 20 years and that the residual value is $30,000, what is the depreciation expense for each of the remaining 20 years