$13.$I want to buy a car. I pay $$506$ per month for five years. The quoted APR is $6\mathrm{.}9\%.$

How much did I pay for the car?

$512=60$ months $6\mathrm{.}9\frac{\%}{12}=0\mathrm{.}5750\%$ per month

$506$

$14.$If the best offer was $$548$ per month from the dealership, how much did they want for the car?

$15.$ What is the balance on the loan after $2\frac{1}{2}$ years, if I made every $$506$ payment on time?

$16.$ How much of payment $2$ is interest? How much goes to principal?

$17.$If I make payments of $$580$ per month, how long will it take me to pay off the loan?