a). 1,600 W = 1.6 kW
15 min = 0.25 hour
(1.6 kW) x (0.25 hr) = 0.4 kW·h
b). If each kW·h of energy costs 7¢ , then 0.4 kW·h costs
(0.4 kW·h) x (7¢ /kW·h) = 2.8¢
