Chapter 3 - Equations and Problem Solving - 3.2 - Equations and Problem Solving - Problem Set 3.2 - Page 106: 24

$a=-4$

Using the properties of equality, the value of the variable that satisfies the given equation, $ 18=-10-7a ,$ is \begin{array}{l}\require{cancel} 18+10=-7a \\\\ 28=-7a \\\\ \dfrac{28}{-7}=a \\\\ -4=a \\\\ a=-4 .\end{array}