Chapter 2 - Equations, Inequalities, and Problem Solving - 2.2 Using the Principles Together - 2.2 Exercise Set - Page 94: 36

$a=-\dfrac{21}{4}$

Using the properties of equality, the solution to the given equation, $ -\dfrac{8a}{7}-2=4 $, is \begin{array}{l} -\dfrac{8a}{7}=4+2 \\\\ -\dfrac{8a}{7}=6 \\\\ a=6\cdot\dfrac{-7}{8} \\\\ a=-\dfrac{42}{8} \\\\ a=-\dfrac{21}{4} .\end{array}