Question

Smallest integer n such that f(x) is O(x^n)?
1. 4x^2+x^3log(x)
2. 7x^5+(logx)^4
3. f(x) = (3x^4+x^2-5)/(7x^4+1)
f(x)=(x^2+3log(x))/(5x^4+1)

I've been trying to do this on my own but I don't really understand Big O notation...
I got:
1. 4
2. 5
3. 0
4. -1