z = -11
Steps:
8z+12 = 5z-21
Subtract 12 from both sides
8z+12-12 = 5z-21-12
Simplify
8z = 5z-33
Subtract 5z from both sides
8z-5z = 5z-33-5z
Simplify
3z = -33
Divide both sides by 3
3z/3 = -33/3
Simplify
z = -11
Hope this helps you! (:
-Hamilton1757