From the text, the relative rate of change of the function P(t) = 3 + 1.6e0.05t is given by P '(t) P(t) = d dt ln(P(t)) . First, we take the natural log, and then take the derivative, using the Chain Rule. ln(P(t)) = ln(3 + 1.6e0.05t) d dt ln(P(t)) = d dt ln(3 + 1.6e0.05t) = 1 d dt (3 + 1.6 e0.05t)