\(x-3y=7\) (1)

\(-3x+4y=-1\) (2)

\(x=7+3y\) (3)

Putting value of \(\displaystyle{x}{\ln{}}\) eq 2

\(-3(7+3y)+4y=-1\)

properly \(\rightarrow -21-9y+4y=-1\)

Combininb like terms \((-5y=20)\)

(Dividing each side by -5) \(\displaystyle{\frac{{{5}{y}}}{{{5}}}}={\frac{{{20}}}{{-{5}}}}\to{y}=-{4}\)

Putting value of y in \(\displaystyle{e}{q}\dot{{\lbrace}}{3}\to{x}\pm{7}+{3}{\left(-{4}\right)}\}\)

\(x=-5\)

\(x-3y=7 | -3x+4y=-1\)

\((-5)-3(-4)=7 | -3(-5)+4(-4)=-1\)

\(7=7 | -1=-1\)

Solution set \(\{-5, -4\}\)