Calculating payments, interest and APR on auto loan. After Careful comparison shopping, Drew redding decides to buy a new toyota camry. With some options added, the car has a price of $23,558-including plates and taxes. Because he can't afford to pay cach for the car, he will use some savings and his old car as a trade in to put down $8,500. He plans to finance the rest with a $15,058.00, 60-month loan at a simple interest rate of 4 percent.