\[\frac{6}{b - 4} - \frac{6b + 1}{b^{2} - 4b} = \frac{6^{\backslash b}}{b - 4} - \frac{6b + 1}{b(b - 4)} =\]
\[= \frac{6b - 6b + 1}{b(b - 4)} = \frac{1}{b^{2} - 4b}\ \]