4. (8 points total) You are thinking of purchasing a house, which costs $400,000. You need to pay 20% down and borrow the remaining 80% of the purchase price. Your bank offers you a 30- year mortgage that requires annual payments and has an annual rate of 3%. (a) what will be the annual payment? (5 points) (b) What will be the loan balance (the amount you still owe) after 15 years? (3 points)