\[\frac{b + 3}{9b - 27} - \frac{b - 1}{b^{2} - 3b} =\]
\[= \frac{b + 3}{9 \cdot (b - 3)} - \frac{b - 1}{b(b - 3)} =\]
\[= \frac{b^{2} + 3b - 9b + 9}{9b(b - 3)} =\]
\[= \frac{b^{2} - 6b + 9}{9b(b - 3)} =\]