## Basic College Mathematics (10th Edition)

$z=-2$
Step 1. Subtract 7z from both sides of the equation. $9+7z-7z=9z-7z+13$ $9=2z+13$ Step 2. Subtract 13 from both sides. $9-13=2z+13-13$ $-4=2z$ Step 3. Divide both sides by 2. $\frac{-4}{2}=\frac{2z}{2}$ $z=-2$