There aren't any numbers that add to 24 but multiply to 9. But you can still factorise - remember, you only need to get numbers that add up to the middle number if the coefficient of y^2 is 1. That means if you just have y^2, not 2y^2 or 3y^2 or 16y^2 like we do here.
16y^2+24y+9 = (4y+3)^2
