The interest rate for the first four years of an $81,000 mortgage loan is 7.5% compounded semiannually. Monthly payments are calculated using a 20-year amortization. a. What will be the principal balance at the end of the four-year term? (Do not round intermediate calculations and round your final answer to 2 decimal places.) Principal balance b. What will be the monthly payments if the loan is renewed at 4.9% compounded semiannually (and the original amortization period is continued)? (Do not round intermediate calculations and round your final answer to 2 decimal places.) Payment per month %24