Calculate :
Knowing :
$\displaystyle \frac{{}^{n} C_k}{n^k} = \frac{n!}{n^k (n-k)! k!} = \frac{n(n-1) \ldots (n-k+1)}{n^k k!} $
Now compare orders of terms in the numerator and denominator. I don't know if you have the answer to work towards, so just to give you a bit more direction here it is if you want it:
Spoiler:
Hope this helps.
pomp.