[tex]\underline{+\left\{\begin{array}{ccc}2x-3y=-9\\-x+3y=6\end{array}\right}\qquad\text{add both sides of the equations}\\.\qquad x=-3\\\\\text{put the value of x to the second equation:}\\\\-(-3)+3y=6\\3+3y=6\qquad\text{subtract 3 from both sides}\\3y=3\qquad\text{divide both sides by 3}\\y=1[/tex]
