4-37 On January 1, Frank bought a used car for $7200 and agreed to pay for it as follows: 1/4 down payment; the balance to be paid in 36 equal monthly payments; the first payment due February 1; an annual interest rate of 9%, compounded monthly. (a) What is the amount of Frank's monthly pay- ment? (b) During the summer, Frank made enough money to pay off the entire balance due on the car as of October 1. How much did Frank owe on October 1