39 persons can repair a road in 12 days, working 5 hours a day. In how many days will 30 persons, of same efficiency working 6 hours a day, complete the work?

None of these

Let's calculate the total man-hours required to complete the work:

39 persons * 5 hours/day * 12 days = 2340 man-hours

If 30 persons work 6 hours a day:

Let x be the number of days they need to complete the work:

30 persons * 6 hours/day * x days = 2340 man-hours

180x = 2340

x = 13