A Factory Machine Was Purchased for $150,000 on January 1

A factory machine was purchased for $150,000 on January 1, 2014. It was estimated that it would have a $30,000 residual value at the end of its 5-year useful life. It was also estimated that the machine would be run 40,000 hours in the 5 years. The company ran the machine for 4,000 actual hours in 2014. If the company uses the units-of-activity method of depreciation, the amount of depreciation expense for 2014 would be

A) $15,000.
B) $24,000.
C) $30,000.
D) $12,000.