$\left\{\begin{array} { l } 3x-8=-2y \\ 2x+y=7\end{array} \right.$
$\left\{\begin{array} { l } -2y=3x-8 \\ 2x+y=7\end{array} \right.$
$\left\{\begin{array} { l } -2y=3x-8 \\ y=7-2x\end{array} \right.$
$\left\{\begin{array} { l } y=-\frac{ 3 }{ 2 }x+4 \\ y=7-2x\end{array} \right.$
$-\frac{ 3 }{ 2 }x+4=7-2x$
$x=6$
$y=7-2 \times 6$
$y=-5$
$\left( x, y\right)=\left( 6, -5\right)$
$\left\{\begin{array} { l } 3 \times 6-8=-2 \times \left( -5 \right) \\ 2 \times 6+\left( -5 \right)=7\end{array} \right.$
$\left\{\begin{array} { l } 10=10 \\ 7=7\end{array} \right.$
$\left( x, y\right)=\left( 6, -5\right)$