13 (4 points) A machine with a cost of $640,000 has an estimated salvage value of $40,000 and an estimated useful life of 5 years or 15,000 hours. It is to be depreciated using the units-of-activity method of depreciation. What is the amount of depreciation for the second full year, during which the machine was used for 5,000 hours? a) $173,333. b) $173,333. c) $200,000. d) $120,000. foll