Explanation:

To solve this problem, let's use the concept of "worker-days," which is the number of workers multiplied by the number of days needed.

- 20 workers paint 24 walls in 36 days.

* Worker-days required for 24 walls = 20 workers × 36 days = 720 worker-days.

- Find worker-days required for 1 wall:

* 720 worker-days for 24 walls means 720/24 = 30 worker-days per wall.

- For 20 walls:

* 30 worker-days per wall × 20 walls = 600 worker-days needed.

- 30 workers need to paint 20 walls:

* 600 worker-days ÷ 30 workers = 20 days.

Therefore, it will take 20 days for 30 workers to paint 20 walls.

Option 1: 20