Explanation

8 men make 18 chairs in 9 days.

First, find out how much work 1 man does in 1 day:

8 men × 9 days = 72 man-days for 18 chairs.

Now, for 27 chairs in 6 days:

Let the number of men be x.

x men × 6 days = 6x man-days.

Compare the two situations:

18 chairs / 72 man-days = 27 chairs / 6x man-days

18 × 6x = 27 × 72

108x = 1944

x = 18