Find the sum and express it in the simplest form.(2y^2+9y+4)+(-3y^2-3y-9)

Since the operation between the two sets of parentheses is addition, we don't have to do anything with it, and can remove the parentheses.
Our new expression is: 2y^2+9y+4-3y^2-3y-9

Now, we just add like terms together to solve for the simplest form of the expression.
2y^2+9y+4-3y^2-3y-9
(2-3)y^2+(9-3)y+(4-9)
-y^2+6y-5

Our final answer is -y^2+6y-5.