用适当的方法解下列方程组：
(1)$\begin{cases}3s - t = 5,\\5s + 2t = 15;\end{cases}$ (2)$\begin{cases}2x - y = 5,\\7x - 3y = 20;\end{cases}$
(3)$\begin{cases}4(x + 2) + 5y = 1,\\2x + 3(y + 2) = 3;\end{cases}$ (4)$\begin{cases}x - 2y = 5,\\2x + 7y = -1;\end{cases}$
(5)$\begin{cases}\dfrac{x}{3} - \dfrac{y}{2} = \dfrac{2}{3},\\\dfrac{x}{4} + \dfrac{y}{4} = -\dfrac{9}{4};\end{cases}$ (6)$\begin{cases}x + y = 1,\\2x - y = -4;\end{cases}$
(7)$\begin{cases}3(x + y) - 4(x - y) = 16,\\\dfrac{x + y}{2} + \dfrac{x - y}{6} = 1;\end{cases}$ (8)$\begin{cases}x + 2y + 3z = 14,\\3x + y + 2z = 11,\\2x + 3y + z = 11.\end{cases}$
答案：(1)$\{ \begin{array} { l } { s = \frac { 25 } { 11 }, } \\ { t = \frac { 20 } { 11 } } \end{array} $ (2)$\{ \begin{array} { l } { x = 5, } \\ { y = 5 } \end{array} $ (3)$\{ \begin{array} { l } { x = - 3, } \\ { y = 1 } \end{array} $ (4)$\{ \begin{array} { l } { x = 3, } \\ { y = - 1 } \end{array} $
(5)$\{ \begin{array} { l } { x = - 4.6, } \\ { y = - 4.4 } \end{array} $ (6)$\{ \begin{array} { l } { x = - 1, } \\ { y = 2 } \end{array} $ (7)$\{ \begin{array} { l } { x = \frac { 1 } { 3 }, } \\ { y = \frac { 7 } { 3 } } \end{array} $ (8)$\{ \begin{array} { l } { x = 1, } \\ { y = 2, } \\ { z = 3 } \end{array} $
