For simple interest we have: A = P*(1+rt)
A is the final Amount (The initial deposit + the interest earned).
P is the initial principle balance. (The initial deposit).
r is the annual interest rate.
and finally t is the time in years.
So your problem gives you A, P, and t.
r is the only thing you don't know.
Some algebra should get you the answer.
Notice though how r is an interest rate, this means if you solve for r and get 0.5. The interest rate is actually 50% not 0.5%.