The solution of a system of equations in the point of intersection of the two lines.
In this case we don't have the point of intersection at first but we notice that the lines are not parallel, hence they have to intersect in some point. To find the intersection we expand the lines in the grid (that is, we continue both lines in both directions). If we do that we get:
Once we find the intersection of both lines we find its coordinates.
Therefore, the solution of the system is the point (-5,-4).