Answer:
x/x+3 
Explanation:
first off, we start by factorizing. 
we start with the numerator taking x out making it x (x-3) / x^2 - 9
then we factorize the denominator a bit more...making it x (x-3) / (x-3) (x+3)
as you can tell there is a (x-3) on both sides. so we can cross them out. 
x/x+3 is left. try it yourself again so you can understand other questions like this! I hope I could help!