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 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. 
let's determine  the administration fee.
=> 810 - 660 dolalrs = 150 dollars is added for additional 3 months.
=> 150 / 3 months = 50 pesos per month.
=> 50 * 12  = 600 dollars.
=> 660 dollars - 600 dollars = 60 dollars is the administration fee.