Answer
$(4,1)$
Work Step by Step
Given system is-
$x -y$ = $3$ __ eq.1
$x +3y$ = $7$ __ eq.2
Subtracting eq.1 from eq.2 -
$(x +3y)-(x -y)$ = $7-3$
i.e. $x +3y-x +y$ = $4$
i.e. $4y$ = $4$
i.e. $y$ = $1$
Substituting for $y$ in eq.1
$x -1$ = $3$
i.e. $x$ = $3+1$ =$4$
Thus $(4,1)$ is the solution of given system.