Answer
$x=\frac{27}{64}$
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, $log_{\frac{3}{4}}x=3$ is equivalent to $(\frac{3}{4})^{3}=x$.
$x=\frac{3}{4}\times\frac{3}{4}\times\frac{3}{4}=\frac{3\times3\times3}{4\times4\times4}=\frac{27}{64}$
