Answer:
Doing the 4th root of x, 3
Explanation:
The opposite of a power is a square root, for example, x to the power of 2's opposite would be the square root of x, since a square root sign has an index of 2. (if you don't know what an index is you can search it up).
to undo the x to the power of 4 you would have to use the square root sign, but change the index of the square root to 4, meaning it would be the 4th root of x.
this means that you are multiplying a number with itself 4 times (rather than only twice when using a normal square root sign) to get 81.
3 would be the answer since 3x3x3x3 is 81 (3x3 is 9, 3x9 is 27, and 27x3 is 81).
I hope this helps
know what Im feeling extra nice, I'll try to explain what an index is.
so a normal square root sign has an index of 2, but it is assumed that is the case, so 2 is not written. however, if you wanted to cube root something, you would have to write the square root sign but with a tiny 3 in the little notch of the square root sign, which signifies that it's the 3rd (more commonly called cubed) root. if you wanted to do the 6th root of a number, you would put a 6 in the little notch to signify that it's the 6th root of a number.
it's a little complicated to explain without being able to draw it so that's why I recommend searching it