Brian invested $950 at the end of every month into an investment fund that was earning interest at 4.50% compounded monthly. He stopped making regular deposits at the end of 10 years when the interest rate changed to 4.75% compounded quarterly. However, he let the money grow in this investment fund for the next 3 years.

a. Calculate the accumulated balance in his investment fund at the end of 10 years.

b. Calculate the accumulated balance in his investment fund at the end of 13 years.

c. Calculate the amount of interest earned over the 13-year period.