20.解下列方程组
(1)$\left\{{\begin{array}{l}{x-2y=0}\\{3x+2y=8}\end{array}}\right.$
(2)$\left\{\begin{array}{l}2x+y=3\\ 3x-5y=11\end{array}\right.$
(3)$\left\{\begin{array}{l}\frac{m}{3}+\frac{n}{6}=2\\ \frac{m}{4}+\frac{n}{4}=2\end{array}\right.$
(4)$\left\{\begin{array}{l}3x+2y=5x+2\\ 2(3x+2y)=2x+8\end{array}\right.$
(5)$\left\{\begin{array}{l}{4(x-y-1)=3(1-y)-2}\\{\frac{x}{2}+\frac{y}{3}=2}\end{array}\right.$.