Resposta:
(9,3)
Explicação passo-a-passo:
[tex]\left \{ {{x-y=6} \atop {x=12-y}} \right.[/tex]
[tex]\left \{ {{12-y-y=6} \atop {x=12-y}} \right.[/tex]
[tex]\left \{ {{12-2y=6} \atop {x=12-y}} \right.[/tex]
[tex]\left \{ {{-y=6-12} \atop {x=12-y}} \right.[/tex]
[tex]\left \{ {{-2y=-6} \atop {x=12-y}} \right.[/tex]
[tex]\left \{ {{y=3} \atop {x=12-y}} \right.[/tex]
[tex]\left \{ {{y=3} \atop {x=12-3}} \right.[/tex]
[tex]\left \{ {{y=3} \atop {x=9}} \right.[/tex]
