Equipment with a cost of $678,700 has an estimated residual value of $72,700, has an estimated useful life of 30 years, and is depreciated by the straight-line method. a. Determine the amount of the annual depreciation. 21,300 X b. Determine the book value at the end of the 12 full years of use. 255,600 X c. Assuming that at the start of the year 13 the remaining life is estimated to be 21 years and the residual value is estimated to be $73,000, determine the depreciation expense for each of the remain 15,300 X