12 persons can complete the work in?
['The job requires= 12 x 18= 216- man-days.', 'In 6- days(6 x12)= 72-man - days of work was completed.', 'The remaining (216–72)= 144 man-days will be completed by (12+4)= 16- men in = 144/16= 9- days.']