Hello, thank you for taking the time to post your question!
I would start by writing out the expression, so based on the information given it should be
b^4 * b^2
when you are multiplying exponents like this together with the same base you can just add them together! So it becomes
b^(4 + 2) = b^6
I hope that helps get you moving in the right direction! Feel free to reach out if you have any additional questions beyond that :)