Work Step by Step
The Conjugate Pairs Theorem says that if a polynomial has real coefficients, then any complex zeros occur in conjugate pairs. That is, if $a + bi$ is a zero then so is $a – bi$ and vice-versa. Its degree is $3$, hence it has $3$ complex (including real) zeros. $2$ zeros are already given, hence there is only $1$ zero left which is $4+i$ (the conjugate of $4-i$) according to the Conjugate Pairs Theorem.