Equipment with a cost of $542,400 has an estimated residual value of $62,400, has an estimated useful life of 20 years, and is depreciated by the straight-line method.

a. Determine the amount of the annual depreciation.

b. Determine the book value after 12 full years of use.

c. Assuming that at the start of the year 13 the remaining life is estimated to be 15 years and the residual value is estimated to be $54,900, determine the depreciation expense for each of the remaining 15 years.