A machine with a cost of $120,000 has an estimated residual value of $15,000 and an estimated life of 5 years or 15,000 hours. It is to be depreciated by the units-of-output method. What is the amount of depreciation for the secand full year, during which the machine was used 5,000 hours? a $45,000 b. $35,000 c. $5,000 d. $21,000