Решите систему уравгегие методом подставте {у=-3х5х+3у=12}

[latex] \left \{ {{y=-3x} \atop {5x+3y=12}} \right. \\ \left \{ {{y=-3x} \atop {5x+3(-3x)=12}} \right. \\ \left \{ {{y=-3x} \atop {5x-9x=12}} \right. \\ \left \{ {{y=-3x} \atop {4x=-12}} \right. \\ \left \{ {{y=-3x} \atop {x=-3}} \right. \\ \left \{ {{y=-3*(-3)} \atop {x=-3}} \right. \\ \left \{ {{y=9} \atop {x=-3}} \right. [/latex]