\[\frac{a}{7} = 20\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \frac{a + 12}{8} = x\]
\[a = 7 \cdot 20\ \ \ \ \ \ \ \ \ \ \ \ \ a = 8x - 12\]
\[140 = 8x - 12\]
\[8x = 152\]
\[x = 19.\]
\[Ответ:x = 19.\]