Hello,
[tex] \left \{ {{3x+2y=-21} \atop {x-3y=4}} \right. \\\\
\left \{ {{3x+2y=-21} \atop {x=4+3y}} \right. \\\\
\left \{ {{3(4+3y)+2y=-21} \atop {x=4+3y}} \right. \\\\
\left \{ {{12+9y+2y=-21} \atop {x=4+3y}} \right. \\\\
\left \{ {{12+11y=-21} \atop {x=4+3y}} \right. \\\\
\left \{ {{11y=-21-12} \atop {x=4+3y}} \right. \\\\
\left \{ {{11y=-33} \atop {x=4+3y}} \right. \\\\
\left \{ {{y=-3} \atop {x=4+3(-3)}} \right. \\\\
\left \{ {{y=-3} \atop {x=5}} \right. \\\\
Sol=\{(5,-3)\}\\\\
[/tex]