Solve the followings (a) A 40-year loan is paid with level annual payments at the end of each year. The principal paid in the 20th payment is 166.59 and the principal paid in the 25th payment is 244.78. Find the interest rate for this loan.
(b) Jane borrows money to buy a new piano. She agrees to pay back the loan with level annual payments at the end of each year for 30 years. The annual interest rate is 7%. The interest in her 10th payment is 366.74. What is the interest in her 20th payment?