Answer
See graph
Work Step by Step
\[\begin{align}
& x+y=4 \\
& \text{*Set }y=0 \\
& x=4 \\
& \text{Plot the point }\left( 4,0,0 \right)\text{ in the plane} \\
& \\
& \text{*Set }x=0\text{ } \\
& y=4 \\
& \text{Plot the point }\left( 0,4,0 \right)\text{ in the plane} \\
& \\
& \text{Graph} \\
\end{align}\]