Answer
$=2$
Work Step by Step
First, we let
$\log_{4}{16} = x$
RECALL:
$\log_b{y} =x \longrightarrow b^x=y$
Use the rule above, where y=16 and b=4, to obtain:
$4^x=16$
Write 16 as $ 4^2$ to obtain:
$4^x=4^2$
Use the rule "If $a^x=a^y$, then $x=y$" to obtain:
$x=2$