Because you want to read at least 12 books, the inequality symbol will be less than or equal to (≤).
You can make the inequality be:
12 ≤ 3x
To solve this inequality divide both sides by 3 to isolate x. And you should get:
12 / 3 ≤ 3x / 3
4 ≤ x
...meaning that you will need to read at least 4 books per month to reach the goal.
