A building with a cost of $180,000 has an estimated residual value of $72,000, has an estimated useful life of 9 years, and is depreciated by the straight-line method. a. What is the amount of the annual depreciation? b. What is the book value at the end of the fifth year of use? c. If at the start of the sixth year it is estimated that the remaining life is 5 years and that the residual value is $50,000, what is the depreciation expense for each of the remaining 5 years