Answer
6y$^3$+y$^2$+7y-20
Work Step by Step
Distribute the negative sign to the parentheses and then combine like terms.
(6y$^3$+2y$^2$-y-11)-(y$^2$-8y+9)
6y$^3$+2y$^2$-y-11-y$^2$+8y-9
(6y$^3$)+(2y$^2$-y$^2$)+(-y+8y)+(-11-9)
6y$^3$+y$^2$+7y-20