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) 12.0 mpg
b) 12.5 mpg
c) 13.0 mpg
d) 13.5 mpg