Question: 12 persons can complete the work in 18 days?
Answer: If 12 men can complete a job in 18 days, it means the job requires the input of 12*18 = 216 man-days. ... So the remaining work can be completed in 144 man-days / 16 men = 9 days. So the work will be completed in 6 + 9 or 15 days from the start or 9 days after the additional 4 men have reported for work.