Question

Write a polynomial function using 3i, 2, -i

Answer 1

Go to wolframalpha.com and type:
expand (x + 3i)(x - 3i)(x + i)(x - i)(x - 2)

You shall see the answer.
If you want to understand how....well:
if 3i is a zero, -3i must also be a zero
if -i is a zero, i must also be a zero
The expression I wrote out above has all of those zeros.
It's a real pain to expand out by hand.
wolframalpha.com does it quickly