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

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

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

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

9d^2 + 3d^3 + 7d^4 -8