Answer
$$(3y-1)(3y+4) .$$
Work Step by Step
First, for the polynomial $9y^2 +9y -4$, we write
$$9y^2 +9y -4=9y^2 - 3y+12y -4 .$$
By grouping the first two terms and the second two terms and then taking out common factors, we have
$$9y^2 - 3y+12y -4=3y(3y-1)+4(3y-1)=(3y-1)(3y+4) .$$
