Answer
-.2
Work Step by Step
We are given $log_{b}3=.5$ and $log_{b}5=.7$.
We know that $log_{b}\frac{x}{y}=log_{b}x-log_{b}y$ (where $x$, $y$, and $b$ are positive real numbers and $b\ne1$).
Therefore, $log_{b}\frac{3}{5}=log_{b}3-log_{b}5=.5-.7=-.2$.