Answer
Please see the graph.
Work Step by Step
Orange line: $x\ge0$
Green line: $y\ge0$
Blue line: $2x+4y\le40$
Since all three lines are either "less than or equal to" or "greater than or equal to", we will shade with solid lines.
Let's use the point $(0,0)$ to determine what side of the lines to shade.
Orange line: $x\ge0$
$x\ge0$
$0 \ge 0$ (true)
This is true, so we shade the side of the line with the point $(0,0)$.
Green line: $y\ge0$
$y\ge0$
$0\ge0$ (true)
This is true, so we shade the side of the line with the point $(0,0)$.
Blue line: $2x+4y\le40$
$2x+4y\le40$
$2*0+4*0\le40$
$0+0 \le 40$
$0 \le 40$ (true)
This is true, so we shade the side of the line with the point $(0,0)$.
We want the intersection of the three graphs, so where all three graphs are shaded is the intersection.
The boundaries of the intersection are $(0,0)$, $(20,0)$, and $(0,10)$ (as shown on the graph).