Answer:
OPTION A: Divide both the sides by 5
Explanation:
We are given: 5z - 3 = 12
When we add 9 to both sides we get:
5z - 3 + 9 = 12 + 9
⇒ 5z + 6 = 21
⇒ 5z = 21 - 6 = 15
⇒ 5z = 15
To find the value of z we have to divide both the sides by 5.
i.e.,

⇒ z = 3.