First of all, we all know that the dog keeps going back and forth between people. We have no way to know how many times it has gone back and forth.

Therefore, we must start from the last time the dog was between them.

So, suppose the dog starts with his brother for the last time.

Because the total time for my brother to go to school is 2/4=0.5h, the total distance the dog walks is 0.5*6=3km.

Suppose the time for my brother to leave the dog for school is t.

So my brother's distance from school at this time is 4t, and the distance he walked before was 2-4t.

The distance the dog has to walk is 6t, and the distance the dog walked before was 3-6t.

And we know that a dog walks 3 kilometers and a brother walks 2 kilometers.

So the dog walks more than his brother 1km.

So between the last separation, the dog walked 3-6t-(2-4t)= 1-2t more than the elder brother.

And then-on your own, that's all I thought of. . . Students, if you know the answer, come on.

You can also talk to me. . . Hey hey. .