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