Answer
Refer to the graph below.
Work Step by Step
Solve for $y$ by subtracting $3x$ to both sides:
$3x+y-3x=0-3x
\\y=-3x$
This means the given equation has the same graph as $y=-3x$.
This equation has:
slope = $-3$
y-intercept: $(0, 0)$
To graph the given equation, perform the following steps:
(1) Plot the y-intercept $(0, 0)$
(2) Use the slope to plot another point.
From $(0, 0)$, move 3 units down (the rise) and 1 unit to the right (the run) to reach $(1, -3)$. Plot $(1, -3)$.
(3) Connect the two points using a line to complete the graph.
(Refer to the attached image in the answer part above for the graph.)