(4 + 7s^3 - 6s^4) + (2s^4 + 8) - (5s^3 - 9s^2)

(4 + 7s^3 - 6s^4) + (2s^4 + 8) - (5s^3 - 9s^2)

4 + 7s^3 - 6s^4 + 2s^4 + 8 - 5s^3 + 9s^2

4+ 8 - 5s^3 + 7s^3 - 6s^4 + 2s^4 + 9s^2

12 + 2s^3 + 5s^2