\[5 \cdot (x - 4) - ax = 6\]
\[5x - 20 - ax = 6\]
\[5x - ax = 6 + 20\]
\[x(5 - a) = 26\]
\[x = \frac{26}{5 - a}\]
\[Ответ:x = \frac{26}{5 - a}.\]