[tex]x-y=3[/tex]
[tex]x+2y=-6[/tex]
Subtract both equations to isolate and solve for y.
[tex](x-x)+(-y-2y)=3-(-6)[/tex]
[tex]0+-3y=9[/tex]
[tex]y=-3[/tex]
Now, solve for x in either equation by plugging in the y value.
I will choose the simpler first equation: [tex]x-y=3[/tex]
[tex]x+3=3[/tex]
[tex]x=0 ; y=-3[/tex]