Question

find a polynomial degree of 3 that has 3, -3, and 9

Answer 1

multiply (x-3)(x+3)(x-9)=y

Answer 2

that has zeros 3,-3, and 9*

Answer 3

after you do (x-3)(x+3) you get x2+3x-3x-9. the 3's cancel out but then what is
left just x or nothing at all?

Answer 4

The 3's cancel out, and you're then left with:
x^2 - 9
Then you multiply that with (x - 9):
(x^2 - 9)(x - 9)
x^3 - 9x^2 - 9x + 81