Answer
$10^{\frac{3log2 log6}{log12}}\approx 4.479$
Work Step by Step
1. $log_2(x)+log_6(x)=3 \Longrightarrow \frac{log(x)}{log2}+\frac{log(x)}{log6}=3\Longrightarrow (\frac{1}{log2}+\frac{1}{log6})log(x)=3 \Longrightarrow log(x)=\frac{3log2 log6}{log12} \Longrightarrow x=10^{\frac{3log2 log6}{log12}}\approx 4.479$
2. Check, $x=10^{\frac{3log2 log6}{log12}}$ fit(s).