a, x . $\dfrac{1}{2}$ = $\dfrac{3}{10}$ . $\dfrac{5}{6}$
$\Leftrightarrow$ x . $\dfrac{1}{2}$ = x . $\dfrac{1}{4}$
`<=>` x = $\dfrac{1}{2}$
b, $\dfrac{x}{5}$ = $\dfrac{-3}{14}$ . $\dfrac{7}{3}$
`<=>` $\dfrac{x}{5}$ = $\dfrac{-1}{2}$
`<=>` $\text{2x = - 5}$
`<=>` $\text{x = $\dfrac{-5}{2}$ }$
c, x + $\dfrac{2}{3}$ = $\dfrac{9}{15}$ . $\dfrac{5}{27}$
`<=>` x + $\dfrac{2}{3}$ = $\dfrac{1}{9}$
`<=>` x = $\dfrac{1}{9}$ - $\dfrac{2}{3}$
`<=>` x = $\dfrac{-5}{9}$
d, x : $\dfrac{4}{11}$ = $\dfrac{11}{4}$ . 2
$\Leftrightarrow$ x : $\dfrac{4}{11}$ = $\dfrac{11}{2}$
$\Leftrightarrow$ x = 2
e, $\dfrac{4}{7}$ x + $\dfrac{2}{3}$ = $\dfrac{1}{5}$
$\Leftrightarrow$ $\dfrac{4}{7}$ x = $\dfrac{1}{5}$ - $\dfrac{2}{3}$
$\Leftrightarrow$ $\dfrac{4}{7}$ x = $\dfrac{-7}{15}$ 
$\Leftrightarrow$ x = $\dfrac{-60}{49}$
f, $\dfrac{2}{9}$ - $\dfrac{7}{8}$x = 1
$\Leftrightarrow$  $\dfrac{7}{8}$x = $\dfrac{2}{9}$ - 1
$\Leftrightarrow$  $\dfrac{7}{8}$x = $\dfrac{-7}{9}$
$\Leftrightarrow$  x = $\dfrac{-8}{9}$
@Meii