Answer
$\dfrac{n+9}{n(n+1)}$
Work Step by Step
As we are given that $\frac{9}{n}-\frac{8}{n+1}$
LCD $= n(n+1)$
$=\dfrac{9(n+1)}{n(n+1)}-\dfrac{8n}{n(n+1)}$
After simplifications, we get
$=\dfrac{9(n+1)-8n}{n(n+1)}$
$=\dfrac{n+9}{n(n+1)}$