(2y^2+9y+4)+(-3y^2-3y)
(2y^2+9y+4)+(-3y^2-3y) the plus sign outside the second set of parentheses doesn't change the signs inside
2y^2 + 9y + 4 - 3y^2 - 3y combine like terms
-1y^2 + 6y + 4