[mat]\left { {{x+y=20} \atop {x-2=y+2}} \right.[/mat]
[mat]\left { {{x=20-y} \atop {20-y-2=y+2}} \right.[/mat]
[mat]\left { {{x=20-y} \atop {-2y=-16}} \right.[/mat]
[mat]\left { {{x=20-y} \atop {y=8}} \right.[/mat]
[mat]\left { {{x=20-8} \atop {y=8}} \right.[/mat]
[mat]\left { {{x=12} \atop {y=8}} \right.[/mat]