Answer
3.9069
Work Step by Step
For all positive numbers $a$, where $a\ne1$, and all positive numbers $x$, we know that $y=log_{a}x$ means the same as $x=a^{y}$.
Therefore, $log_{2}15=x$ means the same as $2^{x}=15$.
By using a calculator to approximate, we know that $x= 3.9069$, because $2^{ 3.9069}=15$.