There's not much to say other that the rule we use is
The c is the index of the root or radical. It's the denominator of the fractional exponent b/c. Comparing terms, we see that a = 3, b = 6 and c = 5.
You could simplify the a^b portion, but it seems like your teacher doesn't want that (right now).
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Side notes:
if c = 2, then we have a square root and often the index number isn't shown at all. So . Its only when c > 2 is when we can't drop the number, or else it'll get mistaken for a square root.
If c = 1, then we won't have any radical. We'll have a^(b/c) = a^b if c = 1.