Find the final amount (rounded to the nearest dollar) in this retirement account, in which the rate of return on the account and the regular contribution change over time. $300 per month invested at 6%, compounded monthly, for first 15 years; then $700 per month invested at 7%, compounded monthly, for next 15 years.

[Hint: 1) You have to find the final amount at the end of 30 years.

2) You will have to do this problem in 3 steps]