x+(x+7)+(x+ 14)= 3x+2 1。
Because x+ 14
X>= 1, then 3x+21> =24.
So there are only 24, 40, 56, 72 possibilities.
Also: when 3x+2 1=40, x= 19/3 is not an integer, so.
3x+2 1 = 56, and x = 35/3 is not an integer.
Therefore, only 24,72 people are eligible.