Answer
$x^4+2x^3+10x^2+18x+9$
Work Step by Step
A zero of $-1$ with multiplicity 2 give factors of $(x+1)^2$,
a complex zero of $3i$ means another zero of $-3i$,
so the function can be written as:
$P(x)=(x+1)^2(x-3i)(x+3i)=(x^2+2x+1)(x^2+9)=x^4+2x^3+10x^2+18x+9$