[tex] \left \{ {{x+2y=12\ \ \ \ \ \ } \atop {-x=-y-6\ \ |*(-1)}} \right. \\\\ \left \{ {{x+2y=12} \atop {x=y+6}} \right. \\\\ using\ substitution \ method\\\\
y+6+2y=12\\
3y+6=12\ \ | subtract\ 6\\
3y=6\ \ | divide\ by\ 3\\
y=2\\
x=y+6=2+6=8\\\\ \left \{ {{y=2} \atop {x=8}} \right.
[/tex]
