The interest rate for a savings fund was 3.70% compounded semi-annualy for the first 4 years and then 4.70% compounded semi-annualy for the second 4 years. Harsha invested $2,400 at the end of each 6 months for 8 years.

a. Calculate the accumulated value of her investment after the first 4 years.

b. Calculate the accumulated value of her investment at the end of 8 years.

c. How much interest did she earn in her investment over the 8 years.