\[3(x - 4) - 5(x + 2) = cx - 6;\ \ \ \]
\[\ x = 6\]
\[3 \cdot (6 - 4) - 5 \cdot (6 + 2) = 6c - 6\]
\[6 - 40 = 6c - 6\]
\[6c = - 34 + 6\]
\[6c = - 28\]
\[c = - \frac{28}{6} = - \frac{14}{3}\]
\[c = - 4\frac{2}{3}\]
\[Ответ:при\ c = - 4\frac{2}{3}.\]