Answer
$x=\frac{1}{64}$
Work Step by Step
If $b\gt0$ and $b\ne1$, then $y=log_{b}x$ means $x=b^{y}$ for every $x\gt0$ and every real number $y$.
Therefore, $log_{4}x=-3$ means $4^{-3}=x$.
We know that $x=\frac{1}{64}$, because $4^{-3}=\frac{1}{4^{3}}=\frac{1}{64}$.
