解答题 （共 6 题 ），解答过程应写出必要的文字说明、证明过程或演算步骤
解方程组 $\left\{\begin{array}{l}3 x-5 y=-1 \\ 4 x+5 y=8\end{array}\right.$
$\left\{\begin{array}{l}3(x-2 y)+8 y=4 \\ \frac{x}{3}+\frac{y}{2}=2\end{array}\right.$
解方程组 $\left\{\begin{array}{l}4 x+y=6 \\ 6 x+y=8\end{array}\right.$
$\left\{\begin{array}{l}3(x+y)-4(x-y)=4 \\ \frac{x+y}{2}+\frac{x-y}{6}=1\end{array}\right.$
$\left\{\begin{array}{c}2 x-y=5 \\ 7 x-3 y=20\end{array}\right.$
$\left\{\begin{array}{c}m-\frac{n}{2}=2 \\ 2 m+3 n=12\end{array}\right.$