答案：$57$
$\left\{ \begin{array}{l}
x+y =456 & \ldots \unicode{x2460} \\
7x =y & \unicode{x2461}
\end{array}\right.$
把 $\unicode{x2461}$ 代入 $\unicode{x2460}$，可得
$\begin{array}{rcl}
x + 7x & = & 456 \\
8x & = & 456 \\
x & = & 57
\end{array}$
