Answer
Please see the graph.
Work Step by Step
Three points on the boundary line are $(0,5)$, $(4,0)$, and $(2,2.5)$. The line is solid since we have a greater than or equal to sign.
$(0,5)$
$5x+4y\le20$
$5*0+4*5\le20$
$0+20\le20$
$20\le20$ (true)
$(4,0)$
$5x+4y\le20$
$5*4+4*0\le20$
$20+0\le20$
$20\le20$ (true)
$(2,2.5)$
$5x+4y\le20$
$5*2+4*2.5\le20$
$10+10\le20$
$20\le20$ (true)
