\[\begin{array}{l} \left( {\frac{7}{{12}} - \frac{2}{3}x} \right):\left( { - \frac{5}{8} + \frac{3}{{10}}} \right) = - \frac{{10}}{{13}}\\ \Leftrightarrow \left( {\frac{7}{{12}} - \frac{2}{3}x} \right):\left( { - \frac{{13}}{{40}}} \right) = - \frac{{10}}{{13}}\\ \Leftrightarrow \frac{7}{{12}} - \frac{2}{3}x = \frac{1}{4}\\ \Leftrightarrow \frac{2}{3}x = \frac{7}{{12}} - \frac{1}{4} = \frac{1}{3}\\ \Leftrightarrow x = \frac{1}{2}. \end{array}\]

`(7/12-2/3x):(-5/8+3/10)=-10/13`

`->(7/12-2/3x):(-50/80+24/80)=-10/13`

`->(7/12-2/3x):(((-50)+24)/80)=-10/13`

`->(7/12-2/3x):(-26/40)=-10/13`

`->(7/12-2/3x):(-13/40)=-10/13`

`->7/12-2/3x=-10/13 . -13/40`

`->7/12-2/3x=((-10).(-13))/(13.40)`

`->7/12-2/3x=130/520`

`->7/12-2/3x=1/4`

`->2/3x=7/12-1/4`

`->2/3x=7/12-3/12`

`->2/3x=(7-3)/12`

`->2/3x=4/12`

`->2/3x=1/3`

`->x=1/3:2/3`

`->x=1/3 . 3/2`

`->x=(1.3)/(3.2)`

`->x=3/6`

`->x=1/2`

Vậy, `x=1/2.`