#### Answer

$3(2x-3)(2x+3)$

#### Work Step by Step

Upon inspection, we find that $3$ is common to all the terms in the expression. Therefore we factor out $3$ from each term of the expression:
$12x^{2}-27$
=$3(4x^{2}-9)$
Next, we further factor the quadratic equation within the parenthesis:
$3(4x^{2}-9)$
=$3[(2x)^{2}-(3)^{2}]$
=$3(2x-3)(2x+3)$