The third method makes use of a graph. Recall that every linear equation with two variables can be represented as a line when pairs of solutions in its solution set are plotted on the graph.
Moreover, EVERY point on the line in the graph corresponds to a pair of values that satisfy the equation for the line.
Now if a pair of values for x and y have to satisfy BOTH the equations in a system, what does it mean graphically?
It means that the point that represents the solution pair of values for the system must lie on BOTH the lines in the graph.
There is only ONE such point for 2 lines. That is the point of intersection of the two lines.
Thus, if we can identify the point of intersection between the two lines in a graph corresponding to the two equation, we can simply read out the x and y values that satisfy the system of the 2 equations from the point.