If 72 men can build a wall of 280 m in length in 21 days, how many men could take 18 days to build a similar type of wall of the length of 100 m?

First, let's find out how many man-days it takes to build a 1 meter length of the wall.

72 men can build 280 m in 21 days, so the total man-days is 72 men * 21 days = 1512 man-days.

Therefore, it takes 1512 man-days to build 280 m, so to build 1 m, it would take 1512 man-days / 280 m = 5.4 man-days.

Now, we want to find out how many men it would take to build a 100 m wall in 18 days.

First, let's find out how many man-days it would take to build a 100 m wall. We know that 1 m takes 5.4 man-days, so 100 m would take 5.4 man-days/m * 100 m = 540 man-days.

If we have 18 days to build the wall, then the number of men required would be 540 man-days / 18 days = 30 men.

So, it would take 30 men 18 days to build a similar type of wall of the length of 100 m.