A typical tractor-trailer will move 18 tons of air per mile at 55 mph. Air resistance increases with speed, causing fuel efficiency to decrease at higher speeds. At highway speeds, a certain truck's fuel efficiency t, in miles per gallon (mpg), can be approximated by t=-0.1 s+13.1, where s is the speed of the truck, in miles per hour (mph). Graph the equation and then use the graph to estimate the fuel efficiency at 66 mph.
a) 12.5 mpg
b) 13.0 mpg
c) 13.5 mpg
d) 14.0 mpg