Answer: y^2 - 6y - 2. To find the sum, add the like-variables. You add them because there is a plus between the two sets of parenthesis. Take away the parenthesis (since there aren’t any factors taken out of either one) and add or subtract accordingly. Since 5y^2 and -4y^2 have the same variable AND exponent, they can be added. The same goes for the -9y and 3y. After adding the like-variables, you should get y^2 - 6y - 2.
