Answer
$\displaystyle \frac{3}{4}$
Work Step by Step
Dividing with $\displaystyle \frac{P}{Q}$ equals multiplying with the reciprocal, $\displaystyle \frac{Q}{P}.$
$\displaystyle \frac{7}{x-5}\div\frac{28}{3x-15}=\frac{7}{x-5}\cdot\frac{3x-15}{28}\qquad$... factor what you can
$=\displaystyle \frac{7}{x-5}\cdot\frac{3(x-5)}{28}\qquad$... divide out the common factors
$=\displaystyle \frac{1}{1}\cdot\frac{3(1)}{(4)}\qquad$
= $\displaystyle \frac{3}{4}$
