`-3/4 . x = 7/16`
$\Leftrightarrow$ `x = 7/16 : -3/4`
$\Leftrightarrow$ `x = 7/16 . -4/3`
$\Leftrightarrow$ `x = -7/12`
$\text{Vậy}$ `x = -7/12`
_____________________
`x : (-3 6/7) = -9/21`
$\Leftrightarrow$ `x : {-27}/7 = -9/21`
$\Leftrightarrow$ `x = -9/21 . -27/7`
$\Leftrightarrow$ `x = 81/49`
$\text{Vậy}$ `x = 81/49`