In order to solve this system, let's use the subtitution method, isolating the variable x in the first equation and then using it in the second equation:
[tex]\begin{gathered} x+y=7\to x=7-y \\ \\ x-3y=-1 \\ (7-y)-3y=-1 \\ 7-4y=-1 \\ -4y=-1-7 \\ -4y=-8 \\ y=\frac{-8}{-4}=2 \\ \\ x=7-y=7-2=5 \end{gathered}[/tex]So the solution for this system is x = 5 and y = 2.
