Answer
$\dfrac{(y-5)}{(y+5)}$
Work Step by Step
Since,in the given rational expressions denominator are same, thus take it as common and add the rational terms simply.
Given: $\dfrac{y^2}{y^2-25}+\dfrac{25-10y}{y^2-25}$
or, $=\dfrac{y^2-10y+25}{y^2-25}$
or, $=\dfrac{(y-5)^2}{y^2-5^2}$
or, $=\dfrac{(y-5)^2}{(y-5)(y+5)}$
or, $=\dfrac{(y-5)}{(y+5)}$
