Answer
$x=3$
Work Step by Step
RECALL:
$\log_a{x}=y \longrightarrow a^y = x$
Use the rule above to obtain:
$\log_4{64}=x
\\\longrightarrow 4^x=64$
Note that $64=4^3$. Thus, the expression above is equivalent to:
$4^x=4^3$
Use the rule $a^m=a^n \longrightarrow m=n$ to obtain:
$x=3$