Martin Company purchases a machine at the beginning of the year at a cost of $78,000. The machine is depreciated using the straight-line method. The machine's useful life is estimated to be 5 years with a $4,000 salvage value. The book value of the machine at the end of year 5 is: a. $14,800. b. $31,200. c. $74,000. d. s0. e. $4,000