Answer
$\displaystyle \frac{1}{27}$
Work Step by Step
For any integer n and any nonzero number $a,$ the number $a^{-n}$ is the reciprocal of $a^{n}$.
So, for $a=3$,
$$\begin{align*}
3^{-3}&=\displaystyle \frac{1}{3^{3}} & & \\
& =\displaystyle \frac{1}{3(3)(3)} \\
&=\displaystyle \frac{1}{27} \end{align*}$$
