Explanation:

- Total work calculation: A and B together complete the work at the rate of \(1/40 + 1/25\) work units per day.

- A's rate: \(1/40\) of work per day.

- B's rate: \(1/25\) of work per day.

- Combined rate of A and B: \(1/40 + 1/25 = (5/200 + 8/200) = 13/200\) of work per day.

- B finishes remaining work in 12 days alone: \((1/25) \times 12 = 12/25\) of the work.

- Amount of work completed by A and B together: \(1 - 12/25 = 13/25\) of the work.

- Days A and B work together: \((13/25) \div (13/200) = 200/25 = 8\) days.

- Correct Answer: Option 1: 8 days

Correct Answer: Option 1: 8 days