An Energy-Efficient Lightbulb Uses 15 W of Power for an Equivalent

An energy-efficient lightbulb uses 15 W of power for an equivalent light output of a 60 W incandescent lightbulb. How much energy is saved each month by using the energy-efficient lightbulb instead of the incandescent lightbulb for 4 hours a day? Assume that there are 30 days in one month.

A) 5.4 kW·hr
B) 1.35 kW·hr
C) 21.6 kW·hr
D) 1.8 kW·hr
E) 7.2 kW·hr