Chapter 1 - Some Basic Concepts of Arithmetic and Algebra - Chapter 1 Review Problem Set - Page 38: 60

$13$

Substituting $a= 3 $ and $b= -4 $, the given expression, $ \dfrac{2a+b}{b+6}-3b ,$ evaluates to \begin{array}{l}\require{cancel} \dfrac{2(3)+(-4)}{-4+6}-3(-4) \\\\= \dfrac{6-4}{2}+12 \\\\= \dfrac{2}{2}+12 \\\\= 1+12 \\\\= 13 .\end{array}