E7-43. (Learning Objective 2: Computing units-of-production depreciation) Buff Gym purchased exercise equipment at a cost of $116,000. In addition, Buff paid $4,000 for a special platform on which to stabilize the equipment for use. Freight costs of $1,800 to ship the equipment were borne by the seller. Buff will depreciate the equipment by the units-ofproduction method, based on an expected useful life of 60,000 hours of exercise. The estimated residual value of the equipment is $12,000. How many hours did Buff Gym use the machine if depreciation expense is $4,680?