Answer
The graphs are parallel lines.
Work Step by Step
RECALL:
(1) In the slope-intercept form of a line's equation, $y=mx+b$, $m$=slope and $b$ is the y-coordinate of the y-intercept.
(2) Parallel lines have equal or the same slope.
Write both equations in slope-intercept form to obtain:
First Equation:
$y=-7x-9$
Second Equation:
$-3y=21x+7
\\\frac{-3y}{-3}=\frac{21x+7}{-3}
\\y=-7x-\frac{7}{3}$
Note that the two equations have the same slope.
Thus, their graphs are parallel lines.