Решите систему уравнений методом подстановки: а) y=-3x 5x+3y=12 б) x=2y+5 2x+3y=-4 (помогите пожалуйста))

[latex] \left \{ {{y=-3x} \atop {5x+3y=12} \right. [/latex] [latex] \left \{ {{y=-3x} \atop {5x+3(-3x)=12}} \right. [/latex] [latex] \left \{ {{y=-3x} \atop {5x-9x=12}} \right. [/latex] [latex] \left \{ {{y=-3x} \atop {-4x=12}} \right. [/latex] [latex] \left \{ {{y=-3x} \atop {x=-3}} \right. [/latex] [latex] \left \{ {{y=-3*(-3)=9} \atop {x=-3}} \right. [/latex] [latex] \left \{ {{x=2y+5} \atop {2x+3y=-4}} \right. [/latex] [latex] \left \{ {{x=2y+5} \atop {2(2y+5)+3y=-4)}} \right. [/latex] [latex] \left \{ {{x=2y+5} \atop {4y+10+3y=-4}} \right. [/latex] [latex] \left \{ {{x=2y+5} \atop {7y=-14}} \right. [/latex] [latex] \left \{ {{x=2y+5} \atop {y=-2}} \right. [/latex] [latex] \left \{ {{x=2*(-2)+5} \atop {y=-2}} \right. [/latex] [latex] \left \{ {{x=1} \atop {x=-2}} \right. [/latex]