(−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.
First you can choose from 26 letters, then from 25 (because you can't use the same letter) then from 24, and then from 23. You multiply 26 * 25 * 24 * 23 and you get your answer.