How do I express a limit to infinity as a definite integral? (Example Inside)

Here’s one of the questions I have:

lim x-> +infinity of:
1/n [ (1/n)^3 + (2/n)^3 + ... + (n/n)^3 ]

I am supposed to express that as a definite integral and then solve using the Fundamental Theorem (that’s the easy step).