#### Problem 14E

14. The graph (from the US Department of Energy) shows how driving speed affects gas mileage. Fuel economy $F$ is measured in miles per gallon and speed $v$ is measured in miles per hour.

(a) What is the meaning of the derivative $F^{\prime}(v) ?$

(b) Sketch the graph of $F^{\prime}(v)$.

(c) At what speed should you drive if you want to save on gas?