Since the Rate of Heat Transfer by Conduction Is Proportional $\Delta$

Multiple Choice

Since the rate of heat transfer by conduction is proportional to the $\Delta$ T, what percent savings in your heating bill would you expect if you turned the thermostat down from 75 $\degree$ to 65 $\degree$ , and the outside temperature is 25 $\degree$ F?

A) 10%
B) 20%
C) 30%
D) 40%
E) 50%