Answer
$3x(x+6)(x-6)$
Work Step by Step
Since $3x$ is common to both of the terms of the equation, we take it out as a common factor:
$3x^{3}-108x=3x(x^{2}-36)$
We simplify the expression further using the rule $a^{2}-b^{2}=(a+b)(a-b)$:
$3x(x^{2}-36)=3x(x^{2}-6^{2})=3x(x+6)(x-6)$
