You put $7,500 into an investment account. The account is projected to earn 9% interest per year.

Question

I don't understand how to set it up into a equation 

Answer 1

You need a clear set of given data, and an applicable formula.

 

Your 'question' is incomplete. For example, it could be that you want to find the resulting amount, after 2 years of simple interest. Or there could be compounding, n times per year, and the question could be how much would have accumulated after five years.

 

Your textbook/class notes will have appropriate financial formulas. But you need a clear statement of what is desired.