The given equations are,
[tex]\begin{gathered} -x+y=4 \\ x+3y=4 \end{gathered}[/tex]Adding the first and second equations, we have,
[tex]\begin{gathered} -x+y+x+3y=4+4 \\ 4y=8 \\ y=\frac{8}{4}=2 \end{gathered}[/tex]Substituting the value of y in first equation, we have,
[tex]\begin{gathered} -x+2=4 \\ -x=4-2 \\ x=-2 \end{gathered}[/tex]