\[7x - 5 \cdot (2x + 1) = 5x + 15\]
\[7x - 10x - 5 = 5x + 15\]
\[- 8x = 20\]
\[x = - \frac{20}{8}\]
\[x = - 2,5.\]
\[Ответ:\ x = - 2,5.\ \]