Question 1087992
First of all, it seems you are mixing dollars and cents.  The fixed cost should be 75, not 0.75. 
Your equations should read:
Plan A: f(m) = 0.20m + 75
Plan B: f(m) = 0.35m
If you wanted to use these to find, for example, at what mileage do the two plans cost the same, you would set the cost equal and solve for m