Answer:
Hi! Alrighty this is a long one so here we go:
You first are going to want to find the like terms then add or subtract those together
3x^4 + 2x - 5x^2 + 4x^2 + 6x - 2x - 3x^4 + 7x - 3x^3
I made the like terms look like eachother if that makes any sense^
So subtract 3x^4 from 3x^4, which just cancels eachother out
2x - 5x^2 + 4x^2 + 6x - 2x + 7x - 3x^3
Now do the next ones which are the ones in bold (it doesnt matter which ones you do but these are the ones im doing)
So if you add those together, you now have
2x - 1x^2 + 6x - 2x + 7x - 3x^3
Add/subtract the bold ones again
13x - 1x^2 - 3x^3 is your answer!
Hope I helped have a good day :)