A factory machine was purchased for $60,000 on January 1, 2020. It was estimated that it would have a $18,000 salvage value at the end of its 5-year useful life. It was also estimated that the machine would be run 30,000 hours in the 5 years. If the actual number of machine hours ran in 2020 was 5,000 hours and the company uses the units-of-activity method of depreciation, the amount of depreciation expense for 2020 would be; a. $6,000 b. $9,600. c. $12,000 d. $7,000