If 20% is the down payment, the 80% (the remaining portion) the amount of the loan. There's a couple ways to do it, but the fastest is Price, multiplied by the loan percentage. In this case:
$86,500 x 80% = $69,200
Another way is to find out what the down payment is (20%) and multiply that by the selling price. Then subtract the original price.
$86,500 x 20% = $17,300
$86,500 - $17,300 = $69,200