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 89%. A B1ueball motor costs $6000 and has an 85% efficiency. Neither motor would have any salvage value, as the cost to remove it would equal its scrap value. The annual maintenance cost for either motor is estimated at. $300 per year Electric power costs $0.072/kilowatt-hour (1 hp = 0.746 kW). If a 10% interest rate is used in the calculations, what is the minimum number of hours the higher initial cost Graybar motor must be used each year to justify its purchase?