#### Answer

$x$

#### Work Step by Step

RECALL:
$\log_b{x}=y \longrightarrow b^y=x$
Let
$\log_b{b^x} = y$
Use the rule above to obtain:
$\log_b{b^x}=y \longrightarrow b^y=b^x$
Use the rule $a^m=a^n \longrightarrow m=n$ to obtain:
$b^y=b^x \longrightarrow y = x$
Thus, the missing expression in the given statement is: $x$