\[\frac{a}{8} = 10\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \frac{a - 3}{7} = x\]
\[a = 8 \cdot 10\ \ \ \ \ \ \ \ \ \ a = 7x + 3\]
\[80 = 7x + 3\]
\[7x = 77\]
\[x = 11.\]
\[Ответ:x = 11.\]