[tex] \left \{ {{3x+2y=7} \atop {y=x-4}} \right.[/tex]
Express [tex]y[/tex] from first equation:
[tex]2y=7-3x[/tex]
[tex]y=\frac{7-3x}{2}[/tex]
Then, replace [tex]y[/tex] in second equation with found value and solve it:
[tex]\frac{7-3x}{2}=x-4[/tex]
[tex]7-3x=2x-8[/tex]
[tex]5x=15[/tex]
[tex]x=15/5=3[/tex]
Now, replace [tex]x[/tex] in first equation with found value and solve it too:
[tex]3*3+2y=7[/tex]
[tex]9+2y=7[/tex]
[tex]2y=-2[/tex]
[tex]y=-2/2=-1[/tex]
So the result is: [tex]x=3[/tex] and [tex]y=-1[/tex]
