Answer
Please see the graph.
Work Step by Step
Let $x=0$
$x+3y=9$
$0+3y=9$
$3y=9$
$3y/3=9/3$
$y=3$
Let $y=0$
$x+3y=9$
$x+3*0=9$
$x=9$
Let $x=6$
$x+3y=9$
$6+3y=9$
$3y=3$
$3y/3=3/3$
$y=1$
Three points on the line are $(0,3), (9,0),$ and $(6,1).$