Explanation:

- Sai can complete the work in 50 days. So, Sai's work rate is 1/50 of the work per day.

- Ria is 25% more efficient than Sai. This means Ria's efficiency is 125% of Sai's.

- To find Ria's efficiency, multiply Sai's work rate by 1.25: (1/50) * 1.25 = 1/40 of the work per day.

- Ria will take 40 days to complete the work alone, since her work rate is 1/40 of the work per day.

- Option 1: 30 days - Not relevant as it's less than the calculated days.

- Option 2: 60 days - Irrelevant, greater than time required.

- Option 3: 40 days - Correct

- Option 4: 56 days - Irrelevant, greater than time required.

Your Answer is RIGHT