Answer:
(3x - y)(3x + y)
Step-by-step explanation:
Both 9x^2 and y^2 are perfects squares.
The rule for factoring perfect squares is a^2 - b^2 = (a - b)(a + b).
Here, factoring (3x)^2 - y^2 results in (3x - y)(3x + y).
