A car rental company's standard charge includes an initial fee plus an additional fee for each mile driven. The standard charge S(in dollars) is given by the function.

S = 16.95+0.50M

M is the miles driven and the company also offers an option to insure the car against damage. The insurnace charge I (in dollars) is given by the function.

I = 3.90+0.15M

Let C be the total charge for the rental that includes insurance. Write the equation relating C to M and Simplify.