Subtract x^3-9x^2-4 from the sum of 9x^3+x^2 and -x^3-6x+8

Step-by-step explanation:

First find the sum. You can only add numbers with the same powers.

(9x^3+x^2) + (-x^3-6x+8)

(9x^3  + - x^3) + (x^2) + (6x) + (8) = 8x^3 + x^2 + 6x + 8

Subtract:

(8x^3 + x^2 + 6x + 8) - (x^3 - 9x^2 - 4)

(8x^3 - x^3) + (x^2 - - 9x^2) + (6x) + (8 - - 4) = 7x^3 + 10x^2 + 6x + 12