how does one go about finding the critical points to this function, given its first and 2nd derivative.

$\displaystyle

\begin{array}{l}

f(b) = \frac{{b + 3}}{{b^2 + 2b}} \\

f'(b) = \frac{{ - b^2 - 6b - 6}}{{b^2 (b + 2)^2 }} \\

f''(b) = \frac{{2(b^3 + 9b^2 + 18b + 12)}}{{b^3 (b + 2)^3 }} \\

\end{array}

$