Answer
$x=-1$
Work Step by Step
RECALL:
$\log_a{x}=y \longrightarrow a^y=x, a\gt0, a\ne1$
Use the rule above to obtain:
$\log_3{(3^x)}=-1 \longrightarrow 3^{-1}=3^x$
Use the rule "$a^m=a^n\longrightarrow m=n$" to obtain:
$-1 = x$