#### Answer

$\frac{-2n-21}{n(n+3)}$

#### Work Step by Step

By inspection, we see that the LCM of the denominators is $n(n+3)$. Therefore, we create a common denominator using this LCM and obtain:
$\frac{5}{n+3}-\frac{7}{n}$
=$\frac{n(5)-7(n+3)}{n(n+3)}$
=$\frac{5n-7n-21}{n(n+3)}$
=$\frac{-2n-21}{n(n+3)}$