Add. your answer should be a polynomial in standard form. ( − 8 y 2 − 9 y ) + ( 8 y 3 + 9 y 2 − 2 y ) =

(−8* y^2−9*y)+(8*y^3+9*y^2−2*y) 
first, remove extraneous parentheses (or distribute if negative)
=−8* y^2−9*y+8*y^3+9*y^2−2*y  
then group terms in decreasing degree of y (variable)
=+8*y^3 −8* y^2+9*y^2  −9*y−2*y
simply expression by adding/subtracting similar terms
=+8*y^3 +y^2  −11*y
to give the final answer.