Intermediate Algebra (6th Edition)

$x=4$
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, $log_{x}64=3$ is equivalent to $x^{3}=64$. We know that $x=4$, because $4^{3}=4\times4\times4=64$.