If s(-2,-7) is the solution to the equations then putting x=-2 and y=-7 in them should satisfy them; but it doesn't!
Take the second equation: x=y-5. When y=-7, x would be -12, but x should be -2.
x=y-5 so 4x=4y-20. We can substitute for 4x in the other equation: 7y-4y+20=29, so 3y=9 and y=3, making x=-2.
Now both equations are satisfied.
Graphically, the two eqns can be represented by two intersecting straight lines. The point s is where they intersect, (-2,3), not (-2,-7).