A 120-V air conditioner unit draws 15 A of current. If it operates for 20 min,
(a) How much energy in kilowatt-hours does it use in that time?
(b) If the cost of electricity is $0.15/kWh, what is the cost (to the nearest penny) of operating the unit for 20 min?
(c) If the air conditioner initially cost $ 450 and it is operated, on average, 4 h per day, how long does it take before the operating costs equal the price?