Answer
{$\frac{1}{2}$}
Work Step by Step
For all positive numbers $a$, where $a\ne1$, and all positive numbers $x$, we know that $y=log_{a}x$ means the same as $x=a^{y}$.
Therefore, $log_{x}64=-6$ means the same as $x^{-6}=64$.
We know that $x=\frac{1}{2}$, because $\frac{1}{2}^{-6}=64$.
