Professor's Annuity Corporation offers a lifetime annuity to retiring professors. For a payment of $72,000 at age 65 , the firm will pay the retiring professor $400 a month until his death. a. If the professor's remaining life expectancy is 20 years, what is the monthly interest rate on this annuity? Note: Do not round intermediate calculations. Enter your answer as a percent rounded to 2 decimal places. b. What is the effective annual interest rate? Note: Do not round intermediate calculations. Round your answer to 2 decimal places. c. If the monthly interest rate is 0.50%, what monthly annuity payment can the firm offer to the retiring professor? Note: Do not round intermediate calculations. Round your answer to 2 decimal places