It must have have 3 zeros. For the coefficients to be real, the complex conjugate of a complex zero must also be a zero. Hence, the 3 zeros are
-3 - i
-3 + i
f(x) = A(x + 4) [x - (-3 - i)] [x - (-3 + i)]
where A is real and A ≠ 0. You can expand to standard form and finish from here.