Assume that you contribute $300 per month to a retirement plan for 25 years. Then you are able to increase the contribution to $500 per month for 20 years. Given a 9 percent interest rate, what is the value of your retirement plan after 45 years?

How can I reach the answer using excel? Below is what I'm tracking but I think I'm off because I was not able to show the value increase of the intial $300 for 25 years. How do I add in the interest increase of the 300 per month for 25 years during the additional 20 years I've contributed 500?

PMT=300, i=9/12=.75, NPER=300 $619,106.43

PMT=500, i=9/12=.75, NPER=240 $333,943.43

$953,049.86