## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$\dfrac{9}{a+3}$
When adding two fractions with common denominators, we add the numerators and copy the denominator. Therefore, $\dfrac{4}{a+3}+\dfrac{5}{a+3} ,$ simplifies to \begin{array}{l}\require{cancel} \dfrac{4+5}{a+3} \\\\= \dfrac{9}{a+3} .\end{array}