How do I work out these:

The numerator (top part) of the fraction behaves as a normal power,
and the denominator (bottom part) represents a root.
For example, the number means:
Take 81, cube it, then find the fourth root.
or
Take 81, find the fourth root, then cube it.
I would recommend the second way, because the numbers will remain smaller
and therefore easier to work with:
So you can work out the answer to your question in the same way:
Answer at the end...
A negative power represent a reciprocal (1 divided by).
For example, the number 2^{1} means:
the reciprocal of 2, or ½.
So you can work out the answer to your question in the same way:
So the answers to your questions are 27 and ¼ respectively.