Answer
$\frac{x}{y+5}$
Work Step by Step
Given : $\frac{5x^{2}}{y^{2}-25} \div \frac{5xy-25x}{y^{2}-10y+25}$
$= \frac{5x^{2}}{(y-5)(y+5)} \times \frac{(y-5)(y-5)}{5x(y-5)}$
$= \frac{x}{y+5}$
(After dividing out the common factors 5x and (y-5))