David received a loan of $51,000, 4 years ago. The interest rate charged on the loan was 4.59% compounded quarterly for the first 9 months, 5.19% compounded semi-annually for the next 2 years, and 5.61% compounded monthly thereafter.

a. Calculate the accumulated value of the loan at the end of the first 9 months.

b. Calculate the accumulated value of the loan at the end of the next 2 year period.

c. Calculate the accumulated value of the loan today.

d. Calculate the amount of interest charged on this loan over the past 4 years.