Explanation:

To solve this, follow the steps:

- Twenty persons work 8 hours a day for 15 days. Total work hours = 20 x 8 x 15.

- This is equal to 2400 hours of work.

- Sixty persons need to complete the same work in 4 days.

- Solve for daily hours per person: (2400 hours) / (60 persons x 4 days).

- This calculation gives you the required hours each day.

Now let's look at the options:

1. Option 1: 11 hours/day

2. Option 2: 12 hours/day

3. Option 3: 9 hours/day

4. Option 4: 10 hours/day

The correct answer:

- Sixty persons should work 10 hours each day to complete the work in 4 days.

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