using a graph tool
case 1)
2x-y=-13
y=x+9
the solution is the point (-4,5)
see the attached figure N 1
case 2)
y=3x-7
y=2x-5
the solution is the point (2,-1)
see the attached figure N 2
case 3)
3x+2y=10
6x-y=10
the solution is the point (2,2)
see the attached figure N 3
case 4)
y=6
x=-5
the solution is the point (-5,6)
see the attached figure N 4
case 5)
4x-3y=5
3x+2y=-9
the solution is the point (-1,-3)
see the attached figure N 5
case 6)
x+y=7
x-y=-1
the solution is the point (3,4)
see the attached figure N 6
the answer in the attached figure