#### Answer

$\color{blue}{2}$

#### Work Step by Step

The rational expressions have the same denominator so they are similar.
Add the numerators and copy the denominator to obtain:
$=\dfrac{b-3+b-15}{b-9}
\\=\dfrac{2b-18}{b-9}$
Factor out $ 2$ in the numerator to obtain:
$\\=\dfrac{2(b-9)}{b-9}$
Cancel the common factors to obtain:
$\\=\color{blue}{2}$