`{-3}/7 - (3/14 - 1 3/7)`
`= {-3}/7 - (3/14 - 10/7)`
`= {-3}/7 + 17/14`
`= 11/14`
___________________
`{-5}/4 + x = 6 2/3 - (3 1/4 + 5 2/3)`
$\Leftrightarrow$ `{-5}/4 + x = 20/3 - (13/4 + 17/3)`
$\Leftrightarrow$ `{-5}/4 + x = 20/3 - 13/4 - 17/3`
$\Leftrightarrow$ `{-5}/4 + x = (20/3 - 17/3) - 13/4`
$\Leftrightarrow$ `{-5}/4 + x = 1 - 13/4`
$\Leftrightarrow$ `{-5}/4 + x = -9/4`
$\Leftrightarrow$ `x = -9/4 + 5/4`
$\Leftrightarrow$ `x = -1`
$\text{Vậy}$ `x = -1`