If you rewrite the first equation, you will see that it becomes
[tex] x = y + 4 \to y = x - 4 [/tex]
i.e. exactly the second equation. This causes the system to be underdetermined, since you're asking for the points of intersection of a line with itself, which means all the points of the line.
To graph it, you should graph twice the line [tex] y = x - 4 [/tex]. To draw it, sample any two points and connect them. For example, choose [tex] x = 4 [/tex] and [tex] x=5 [/tex] to get, respectively, [tex] y=0 [/tex] and [tex] y=1 [/tex]. Then, draw the points [tex] (4,0) [/tex] and [tex] (5,1) [/tex] and connect them.
