Answer
{4}
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, $log_{\pi}\pi^{4}=x$ means the same as $\pi^{x}=\pi^{4}$.
We know that $x=4$, because $\pi^{4}=\pi^{4}$.