You have found your dream house. The selling price is 120,000. You will put $20,000 down and obtain a 25-year fixed-rate mortgage at 8.25% (APR compounded semiannually) for the rest. You plan to prepay the loan by making an additional payment each month along with your regular payment. How much extra must you pay each month if you wish to pay off the load in 20 years? (Assume there is no early payment penalty).