CALCULUS QUESTION...(Growth Rate)?

G(t) = 9000 / 1+22e^ -1.2(t) Where G(t) is the population after t years. Find the Point at which the growth rate of this population begins to decline. I believe this is a question asking for the relative maxima by finding G' (t) and solving for the critical values of t, but I can't seem to get the correct critical values. Can someone help please?