Question

Z-12 / 3=4

Answer 1

Without the use of brackets, the question is ambiguous

If you meant it the way you typed it....
z - 12/3 = 4
z - 4 = 4
z = 8

if you meant
(z-12)/3 = 4
multiply both sides by 3
z - 12 = 12
z = 24

You decide.