[tex]~\ \ \qquad\quad \frac25x+21\ =\ -\frac15(8x-25)-2x\\\\~\qquad\qquad\frac25x+21\ =\ -\frac15\cdot8x-(-\frac15)\cdot25-2x\\\\~\qquad\qquad\frac25x+21\ =\ -\frac85x+5-2x\\\\~\quad\qquad\underline{+\frac85x+2x\ \qquad+\frac85x+2x\quad\ }\\\\ \frac25x+\frac85x+2x+21\ =\ 5\\\\\underline{~\qquad\qquad\quad-21\qquad\ -21\ }\\\\~\ \qquad\qquad\frac{10}5x+2x\ =\ -16\\\\~\ \qquad\qquad2x+2x\ =\ -16\\\\~\quad\qquad\qquad4x\ =\ -16\\\\~\ \qquad\qquad \underline{\ :4\qquad\ \ :4\ \ }\\\\~\quad\qquad\qquad x\ =\ -4[/tex]
