[tex]\begin{gathered} \begin{bmatrix}-3x+6y=15 \\ y=2x+4\end{bmatrix} \\ -3x+6\mleft(2x+4\mright)=15 \\ -3x+12x+24=15 \\ 9x+24=15 \\ 9x+24-24=15-24 \\ 9x=-9 \\ \frac{9x}{9}=\frac{-9}{9} \\ x=-1 \end{gathered}[/tex]
then solve for y
[tex]\begin{gathered} y=2x+4 \\ y=2\mleft(-1\mright)+4 \\ y=-2+4 \\ y=2 \end{gathered}[/tex]
