A 200-W computer power supply is on 10 h per day.
(a) If the cost of electricity is $0.15/kWh, what is the energy cost (to the nearest dollar) if this computer is used like this for a year (365 days)?
(b) If this power supply is replaced by a more efficient 100-W version and it costs $ 75, how long will it take the decreased operating cost to pay for this power supply?