A car rental company charges an initial fee plus an additional fee for each mile driven. The charge depends on the type of car: economy or luxury. The charge E (in dollars) to rent an economy car is given by the function E =0.80 M+11.95, where M is the number of miles driven. The charge L (in dollars)
to rent a luxury car is given by the function L=1.15 M+21.40.
Let C be how much more it costs to rent a luxury car than an economy car (in dollars). Write an equation relating C to M. Simplify your answer as much as
possible.