(3x^4-6x-5x^2+5) + (6x^2-4x^3-1+7x)

Well, there's no much that is difficult here, no expansions..

I'll give you an example instead.

(2x^2+5x^6 - 2x +5) + (2 -5x +4x^2 -5x^3) - (5x + 5x^3 - 2x^2) =2x^2+5x^6 - 2x +5 + 2 -5x +4x^2 -5x^3 - 5x - 5x^3 + 2x^2

OOOOOOOOOOOOOOOOOOOOOOOOOiOOOOOOOOOOOOOOOOOO =5x^6 -5x^3- 5x^3+2x^2+4x^2+ 2x^2 - 2x -5x- 5x+ 2 +5

OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO =5x^6 -10x^3+8x^2 - 12x +7

See? Groupd all the similar together, then it's easy.