Hello, thank you for taking the time to post your question!
The key on this type of question is to set up an algebraic expression that represents the information given in the question. On this one we have
A = P(1 + r)^t since you want to apply the compound interest formula
For Kevin that becomes
A = 9000(1 + 0.029)^11 = $12,325.70 at the 2.9% rate of return
Then for Charles that becomes
A = 9000(1 + 0.055)^11 = $16,218.83 at the 5.5% rate of return
So after 11 years Charles has
$16,218.83 – $12,325.70 = $3,893.13 more than Kevin
I hope that helps you get moving in a better direction on this type of question! Feel free to reach out if you have any additional questions beyond that :)
