Explanation:

- A completes work in 30 days, so A does 1/30 of the work per day.

- B is 25% more efficient than A, thus B does 1.25 * (1/30) = 1/24 of the work per day.

- C is 20% more efficient than B, so C does 1.2 * (1/24) = 1/20 of the work per day.

- Together, they do (1/30 + 1/24 + 1/20) = 1/8 of the work per day.

- In 3 days, they complete 3 * (1/8) = 3/8 of the work.

- Remaining work is 1 - 3/8 = 5/8.

- B alone completes 1/24 of the work per day.

- To finish 5/8 of the work, B takes (5/8) / (1/24) = 15 days.

- Therefore, the correct option is:

Option: 4 - 15 days