The general equation that may be used to determine the total cost of the parking permit, P = A + mt where P is the total cost, A is the administration fee, m is the monthly fee and t is the number of months. Substituting the known values to the equation, (1) 660 = A + 12m (2) 810 = A + 15 m
Solving for the solutions of the equation gives A = 60 and m = 50. Thus, the administration fee is $60.