Answer
$(b)$
Work Step by Step
For $x\gt 0$ and $a$ = a positive constant other than 1,
$\log_{a}x$ is the exponent to which $a$ must be raised in order to get $x$.
Thus, $\log_{5}(5^{x})=m$ means $5^{m}=5^{x}$
so, $m= \log_{5}(5^{x})= x$
case $(b)$