#### Answer

Refer to the image below for the graph.

#### Work Step by Step

Add 18 on both sides of the equation to obtain:
$3x=18$
Divide 3 on both sides to obtain:
$x=6$
RECALL:
(1) The graph of the equation $x=h$ is a vertical line whose x-intercept is $h$.
(2) The graph of the equation $y=k$ or $f(x) =k$ is a horizontal line whose y-intercept is $k$.
The equation above is similar to the form in (1) above.
Thus, its graph is a vertical line whose x-intercept is $6$.
(refer to the attached image in the answer part above for the graph)