Chapter 3 - Equations and Problem Solving - 3.2 - Equations and Problem Solving - Problem Set 3.2 - Page 106: 23

$a=-2$

Using the properties of equality, the value of the variable that satisfies the given equation, $ 16=-2-9a ,$ is \begin{array}{l}\require{cancel} 16+2=-9a \\\\ 18=-9a \\\\ \dfrac{18}{-9}=a \\\\ -2=a \\\\ a=-2 .\end{array}