If a polynomial function f(x) has roots -8,1 and 6i what must be the root of f(x)

I think you meant:  "If a polynomial function f(x) has roots -8,1 and 6i what must be the 4th root of f(x)?"

Since complex roots always come in pairs, the 4th root would be - 6i.

The mode of the numbers is 29.