Answer
$(-3)^{12}$
Work Step by Step
Based on the product rule for exponents, we know that $a^{m}\times a^{n}=a^{m+n}$ (where $m$ and $n$ are positive integers and $a$ is a real number).
Therefore, $(-3)^{3}\times(-3)^{9}=(-3)^{3+9}=(-3)^{12}$.