Explanation:

To solve this problem, follow these points:

- First calculate the total work done in terms of "boy-hours."

- 42 boys * 20 days * 8 hours/day = 6,720 boy-hours.

- Now, find out how many days 14 boys working 12 hours a day would take to complete the same amount of work.

- Calculate the number of working hours in a day for 14 boys:

- 14 boys * 12 hours/day = 168 boy-hours per day.

- To find the number of days needed:

- Total work / daily work = 6,720 boy-hours / 168 boy-hours per day = 40 days.

- Therefore, the correct answer is option:2, 40 days.

Answer?: 40 days

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