Question

Help I do not understand

Answer 1

$\bf \begin{cases} f(x)=\cfrac{x}{x-9} \\ \quad \\ g(x)=\cfrac{-x}{x-3} \end{cases}\qquad f(x)+g(x)\implies \cfrac{x}{x-9}+\cfrac{-x}{x-3}$

get their LCD, like you'd with any other fractions, and add them up