Answer
$\dfrac{(y-3)}{(y+3)}$
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: $\dfrac{y^2}{y^2-9}+\dfrac{9-6y}{y^2-9}$
or, $=\dfrac{y^2+9-6y}{y^2-9}$
or, $=\dfrac{(y-3)^2}{y^2-3^2}$
or, $=\dfrac{(y-3)^2}{(y-3)(y+3)}$
or, $=\dfrac{(y-3)}{(y+3)}$
