Answer:
16
Explanation:
Assuming binary attendees, the sum of men and women is 37; the difference of women and men is 5. The number of men is ...
(37 -5)/2 = 16
16 men were there.
_____
Additional comment
21 women were there, for a total of 16+21 = 37.
This form of problem is what I call a "sum and difference" problem. The solution is always the same. For positive values of sum and difference, the smaller of the two numbers is half the difference of the given values, as we showed above.
w +m = s . . . . sum
w -m = d . . . . difference
(w +m) -(w -m) = s - d . . . . . the difference of the two equations
2m = s -d . . . . . . . . . . . . simplified
m = (s -d)/2 . . . . . . . . the formula described above