Answer
$3y(y-4)(y+4)$
Work Step by Step
Factor out $3y$ to obtain:
$=3y(y^2-y16)$
Write 16 as $4^2$ to obtain:
$=3y(y^2-4^2)$
The binomial is a difference of two squares.
RECALL:
A difference of two squares can be factored using the formula:
$a^2-b^2=(a-b)(a+b)$
Factor the difference of two squares using the formula above with $a=y$ and $b=4$ to obtain:
$=3y(y-4)(y+4)$
