Vanessa invested $650 at the end of every month in an investment fund that was earning interest at a rate of 4.74% compounded monthly. She stopped making regular deposits at the end of 9 years when the interest rate changed to 6.72% compounded quarterly. However, she let the money grow in this investment fund for the next 3 years.

a. Calculate the accumulated balance in her investment fund at the end of 9 years.

b. Calculate the accumulated balance in her investment fund at the end of 12 years.

c. Calculate the total interest earned over the 12-year period.