Answer
Answers may vary. One system of equations is
$x+y=7$
$x-y=-3$
Work Step by Step
Green line: $x+y=7$
Purple line: $x-y=-3$
$x-y=-3$
$x=y-3$
$x+y=7$
$(y-3)+y=7$
$2y-3=7$
$2y=10$
$2y/2=10/2$
$y=5$
$x=y-3$
$x=5-3$
$x=2$