Next time, please include the directions for the problem you post. Here it appears that you have given the values of I, P and t two times each.
Unfortunately, I have to guess what you're looking for.
Assuming that I=$26.25 is the interest earned on Principal P=$500, and that t is the length of time over which the Principal earns interest,
I=Prt. With I, P and t given, it's obvious that our job is to find the annual interest rate, r. So, from I=Prt, we get
$26.25 = $500 (r) (1.5 years) Solve this for the interest rate, r.
Express r both as a decimal fraction and as the equivalent percentage.