Please answer the ??? on questions A, B, and C

A. Find the final amount in the following retirement account, in which the rate of return on the account and the regular contribution change over time.

$678 per month invested at 6%, compounded monthly, for 3 years; then $784 per month invested at 7%. compounded monthly for 3 years.

What is the amount in the account after 6 years ??? (Round to the nearest dollar as needed.)

B. Find the final amount in the following retirement account, in which the rate of return on the account and the regular contribution change over time.

$1300 per quarter invested at 4.2%, compounded quarterly for 10 years; then $1900 per quarter invested at 4.4% compounded for 16 years.

Find the final amount in the account.??? (Round to the nearest dollar as needed.)

C. Find the interest rate needed for the sinking fund to reach the required amount. Assume that the compounding period is the same as the payment period.

$60,000 to be accumulated in 9 years; annual payments of $5047.

The interest rate needed is approximately ??? % (Round to two decimal places as needed.)