Answer:
If we consider real numbers, there is no solution.
If we take into account imaginary numbers, there are 2 solutions.

Explanation:
We can take 64 to the other side and then take the square root.
Thus, we have:

We CANNOT take the square root of a negative number, so there is no solution.
BUT, if we take into account Imaginary Numbers, we can solve:

Where

AND, we can take the positive and negative versions of 8i, since squaring would take it back to original.
So the answer would be 8i and -8i