Ok so basically I need to find the interest rate. Here's my work so far:

Using the formula A=P(1+i)^n

P = 4000, A = 5983.66, m = 4, t = 9, r = r/4, n = 36.

So I plug it in and eventually I get to:

(5983.66/4000)^1/36 - 1 = r/4

How do I calculate this so that my answer isn't negative? I put it in the calculator and it comes up completely wrong. I'm gonna have to ask you to have patience with this one and tell me how you put it on the calculator because I'm a bit confused. Thanks for your help