Explanation

6 people dig a 200m well in 15 days.

To find the total work done in terms of "man-days":

6 people × 15 days = 90 man-days

Now, let's find the number of people required to dig the same well in 18 days:

Let x be the number of people required.

x people × 18 days = 90 man-days

x = 90 / 18

x = 5