The unpaid balance of an installment loan is equal to the present value of the remaining payments. The unpaid balance, P, is given by the formula below where PMT is the regular payment amount, r is the annual interest rate, n is the number of payments per year, and t is the number of years remaining in the loan. Complete parts a. and b. below. -nt P=PMT - - | - A a. Use the loan payment formula to derive the unpaid balance formula. Explain how to derive the unpaid balance formula. Choose the correct answer below. nt Multiply both sides of the loan payment formula by A b. The price of a car is $20,000. You have saved 25% of the price as a down payment. After the down payment, the balance is financed with a 6-year loan with monthly payments at 7%. Determine the unpaid balance after three years. The unpaid balance after three years is $ (Round to the nearest dollar as needed.)