A motor with a 200-horsepower output is needed in the factory for intermittent use. A Graybar motor costs $7000 and has an electrical efficiency of 90%. A blueball motor costs $6000 and has an 85% efficiency.......

The answer is: 160hrs (assume 20year life)

Please show the work to get to that answer.

9-83 A motor with a 200-horsepower output is needed in the factory for intermittent use. A Graybar motor costs $7000 and has an electrical efficiency of 90% A Blueball motor costs $6000 and has an 85% effi- ciency. Neither motor would have any salvage value, since the cost to remove it would equal its scrap value. The annual maintenance cost for either motor is estimated at $500 per year. Electric power costs $0.12/kWh (1 hp 0.746 kW). If an 18% interest rate is used in the calculations, what is the mini- mum number of hours the higher initial cost Graybar motor must be used each year to justify its purchase