In this problem, you can set a variable for each of the three groups, so that the relationship is clear.

Let the first group be x, the second group be y and the third group be z.

So from the meaning of the question, x+3=z-3, y+4-(x-4)=8,

So z=x+6, x = y.

So if the first group has X people, then the second group has X people and the third group has x+6 people.

So it turns out that the third group has the largest number of people, six more than the other two groups.