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

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

4 - 2b^3 + 9b^4 - 6b^4 + 8 - 3b^3 - 7b^2

4+ 8 - 3b^3 - 2b^3 + 9b^4 - 6b^4 - 7b^2

12 - 5b^3 + 3b^4 - 7b^2