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

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

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

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

5n^3 + 2n^2 -6