Answer:
7x^3 + 10x^2 + 6x + 12
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
