If the finance charge (Interest) on a copier is $1,778.00 and the loan for the copier was to be paid in 18 monthly payments. Find the interest refund if it is paid off after the 8th monthly payment is made. Step 1 Find the balance remaining. Step 2 Calculate the total finance charge. Step 3 Find the number of payments remaining. Step 4 Set up the rebate fraction. Step 5 Calculate the rebate amount of the finance charge. Step 6 Calculate the payoff.