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+0.60M11.95, where M is the number of miles driven. The charge L (in dollars) to rent a luxury car is given by the function =L+1.25M21.40.

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.