Explanation:

- Initial Calculation: 15 boys earn Rs900 in 5 days.

- Per Boy Per Day: Find earnings per boy per day:

Rs900 / (15 boys * 5 days) = Rs12

- 20 Boys For 7 Days: Calculate total earnings for 20 boys in 7 days:

20 boys * 7 days * Rs12 = Rs1,680

- ? Option 2 - Rs1,680 is the correct answer.

- Option 1 - Rs1,580, Option 3 - Rs1,540, and Option 4 - Rs1,650 are incorrect based on the calculation.