9. 解下列二元一次方程组：
(1) $\begin{cases}7x - 3y = 9,\\-5x + 6y = -6;\end{cases}$
(2) $\begin{cases}4x - 2y = 7.2,\\7x + 4y = -9.9;\end{cases}$
(3) $\begin{cases}3x + 2y = 8,\\\dfrac{x}{2} - \dfrac{y - 1}{4} = 1;\end{cases}$
(4) $\begin{cases}4(x - y) = 3(2 - y) + 4,\\\dfrac{x}{2} + \dfrac{y}{3} = 4.\end{cases}$

(1) $\begin{cases}7x - 3y = 9,①\\-5x + 6y = -6,②\end{cases}$
①×2得：$14x - 6y = 18,③$
②+③得：$9x = 12$，解得$x = \dfrac{4}{3}$
将$x = \dfrac{4}{3}$代入①得：$7×\dfrac{4}{3} - 3y = 9$，解得$y = \dfrac{1}{9}$
$\therefore \begin{cases}x = \dfrac{4}{3},\\y = \dfrac{1}{9}\end{cases}$
(2) $\begin{cases}4x - 2y = 7.2,①\\7x + 4y = -9.9,②\end{cases}$
①×2得：$8x - 4y = 14.4,③$
②+③得：$15x = 4.5$，解得$x = 0.3$
将$x = 0.3$代入①得：$4×0.3 - 2y = 7.2$，解得$y = -3$
$\therefore \begin{cases}x = 0.3,\\y = -3\end{cases}$
(3) $\begin{cases}3x + 2y = 8,①\\\dfrac{x}{2} - \dfrac{y - 1}{4} = 1,②\end{cases}$
②×4得：$2x - (y - 1) = 4$，即$2x - y = 3,③$
由③得$y = 2x - 3,④$
将④代入①得：$3x + 2(2x - 3) = 8$，解得$x = 2$
将$x = 2$代入④得：$y = 1$
$\therefore \begin{cases}x = 2,\\y = 1\end{cases}$
(4) $\begin{cases}4(x - y) = 3(2 - y) + 4,①\\\dfrac{x}{2} + \dfrac{y}{3} = 4,②\end{cases}$
①化简得：$4x - 4y = 6 - 3y + 4$，即$4x - y = 10,③$
②×6得：$3x + 2y = 24,④$
由③得$y = 4x - 10,⑤$
将⑤代入④得：$3x + 2(4x - 10) = 24$，解得$x = 4$
将$x = 4$代入⑤得：$y = 6$
$\therefore \begin{cases}x = 4,\\y = 6\end{cases}$

10. 如图，在长为 $10\ \mathrm{m}$、宽为 $8\ \mathrm{m}$ 的长方形地块中，沿平行于长方形各边的方向分割出三个一样的小长方形花圃(阴影部分)，求小长方形花圃的长和宽.

设小长方形的长为$x\ \mathrm{m}$，宽为$y\ \mathrm{m}$。
根据题意，得：
$\begin{cases}2x + y = 10 \\x + 2y = 8\end{cases}$
由第一个方程得：$y = 10 - 2x$，代入第二个方程：
$x + 2(10 - 2x) = 8$
$x + 20 - 4x = 8$
$-3x = -12$
$x = 4$
将$x = 4$代入$y = 10 - 2x$，得：
$y = 10 - 2×4 = 2$
答：小长方形花圃的长为$4\ \mathrm{m}$，宽为$2\ \mathrm{m}$。