When rationalizing the denominator when the denominator is a square root, you simply multiply the numerator and denominator by whatever is under the radical sign.
2/sqrt(3) , multiply by sqrt(3)/sqrt(3) to get 2sqrt(3)/3
When you have a higher root, like the cube root, 4th root and so on, the process is a little more complex.
Suppose you have 4/cuberoot(6).. we have to multiply by whatever will make a perfect cube under the radical.. so in this case we multiply by cuberoot(6 * 6) because that will give 3- 6's under the radical which makes cube root of 216 = 6
So the answer is 4cuberoot(6)/6, simplified to 2cuberoot(6)/3.
Same thing applies if there are variables in the denominator under the radical.. if you have cuberoot(x) you need to multiply by cuberoot(x^2) which makes cuberoot(x^3) = x.