Find the least integer n such that f(x) is O (xn) for each of these functions

Find the least integer n such that f(x) is O (xn) for each of these functions.

a)f(x) = 2x2 + x3 logx

b)f(x) = 3x5 + (log x)4

c)f(x) (x4 + x2 + 1)/ (4 + 1)

d)f(x) = (x3 + 5logx)/(x+i)