General form for an exponential:
f(x) = a·bx
where a is the initial or starting value, b is the growth/decay factor. It is growth if b >1, decay if b <1. What are the values of a and b in your equation?
b can be expressed as b = (1 + rate), where rate is the growth or decay rate. It's growth if rate > 0, decay if rate < 0. Plug in the value of b and solve for the rate.