\[\boxed{\text{179\ (179).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\left( \frac{a - 5}{a^{2} - 5a + 25} - \frac{12a - 61}{a^{3} + 125} \right)\ :\]
\[:\frac{3a - 18}{2a^{2} - 10a + 50} =\]
\[= \frac{a^{2} - 12a + 36}{a + 5} \cdot \frac{2}{3 \cdot (a - 6)} =\]
\[= \frac{(a - 6)^{2}}{a + 5} \cdot \frac{2}{3 \cdot (a - 6)} =\]
\[= \frac{(a - 6) \cdot 2}{(a + 5) \cdot 3} =\]
\[= \frac{2a - 12}{3a + 15}\]
\[\boxed{\text{179.}\text{\ }\text{ОК\ ГДЗ\ -\ домашка\ на\ 5}}\]
\[\textbf{а)}\]
\[\textbf{б)}\ \]