Because there are no more or less than 3 columns, circle the multiples of 3;
Because there are 2 less than 5 columns, from the circled numbers, choose the number that is divisible by 3 by 5, and then make a note of it;
Because there are 4 fewer than 7 columns, choose the number that is divisible by 3 by 7 by 7, and then make a note of it. There should be only one.
Answer:*** There are 108 people.
This is a very crude solution, but please take it.