3x+12y-9x-18y=06x+42y+4x+4y=96

[latex] \left \{ {{-6x-6y=0|:(-6)} \atop {10x+46y=96|:2}} \right. \\ \left \{ {{x+y=0} \atop {5x+23y=48}} \right. \\ \left \{ {{x=-y} \atop {-5y+23y=48}} \right. \\ 18y=48 \\ y= \frac{48}{18}= \frac{8}{3} \\ \left \{ {{y= \frac{8}{3} } \atop {x=- \frac{8}{3} }} \right. [/latex]