Explanation:
what is the problem ?
the solution of such a system of 2 equations is the point, where they cross.
this point has the same coordinates for both equations, and that is called the solution.
and we can clearly see that point in the graph :
(-1, 1)
formally we can solve that way
y = 2x + 3
y = -x
therefore,
2x + 3 = -x
3x + 3 = 0
3x = -3
x = -1
y = -x = - -1 = 1
so, we get
(-1, 1) as solution.