Find the remaining zero x^3-6x^2+36x-218 zero: -6i

I know this isn't fair, but I happen to know that imaginary or complex roots always
occur in conjugate pairs.  So if -6i is a root, then +6i also must be one.

The expression also has one real root.

It's between 6.02765006 and 6.02765007 .

The reason for that is probably a mis-type or mis-copy in the question.
The ' 218 ' at the end was probably supposed to be ' 216 '.  In that case,
the real root would have been exactly ' 6 '.