#### Answer

( please see image)

#### Work Step by Step

To graph a line, find two points that belong to it.
x-intercept (y=0)
$3(0) +7x=-21$
$-7x=-21$
$x=3$
Point: $(3,0)$
y-intercept$ (x=0):$
$3y-7(0)=-21$
$3y=-21$
$y=-7$
Point: $(0,-7)$
Plot the two points and draw a line through them.
( please see image)