\[\frac{9}{b^{2} + 3b} - \frac{3}{b} = \frac{9}{b(b + 3)} - \frac{3^{\backslash b + 3}}{b} =\]
\[= \frac{9 - 3 \cdot (b + 3)}{b(b + 3)} = \frac{9 - 3b - 9}{b(b + 3)} =\]
\[= \frac{- 3b}{b(b + 3)} = - \frac{3}{b + 3}\]