Answer
1.2
Work Step by Step
We are given $log_{b}3=.5$ and $log_{b}5=.7$.
We know that $log_{b}xy=log_{b}x+log_{b}y$ (where $x$, $y$, and $b$ are positive real numbers and $b\ne1$).
Therefore, $log_{b}15=log_{b}(5\times3)=log_{b}5+log_{b}3=.7+.5=1.2$.