A car rental company charges an initial fee plus 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=15.95+0.70M, where M is the number of miles driven. The charge L in dollars to rent a luxury car is given by the function L=16.40+1.15M. Let C be how much more it cost 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.

C= ???