Answer
$3(x+3)(x-4)$
Work Step by Step
$3x^2-3x-36\longrightarrow$ 3 is a common factor
$=3(x^2-x-12)$
$=3(\ \ \ \ \ \ \ \ )(\ \ \ \ \ \ \ \ )$
$=3(x\ \ \ \ \ \ )(x\ \ \ \ \ \ )$
$=3(x+\ )(x-\ )$ The factors of -12 must have unlike signs.
$=3(x+3)(x-4)$ 3 and -4 have a sum of -1 and a product of -12.
