The cost of a parking permit consists of a one time administration fee plus a monthly fee. a permit purchased for 12 months costs 660. a permit purchased for 15 months costs 810. what is the administration fee

The administration fee is $60. To do this, you need to find the rate of increase, or cost per month. Start by subtracting 810 by 660, to find the change of cost in 3 months. This will give you a cost of $150 for 3 months. To find the monthly fee, divide by 3, and you will get $50 a month. Now, you can subtract the total of the monthly cost for 12 months, which is $600, from $660, to get the administration fee of $60.

The equations are 660=12x+a and 810=15x+a, where x is the monthly fee and a is the one time administration. You then must subtract both equations to get 150=3x. Then simplify to get 50=x. Now that you have the monthly rate, you plug it into either equation to get the administration fee.
660=12(50)+a
660=600+a
60=a