#### Answer

$(y-3)(y+3)$

#### Work Step by Step

RECALL:
A difference of two square can be factored using the formula
$a^2-b^2=(a-b)(a+b)$
The given binomial can be written as:
$=y^2-3^2$
The binomial above is a difference of two squares.
Factor the difference of two squares using the formula above with $a=y$ and $b=3$ to obtain:
$=(y-3)(y+3)$