Since average will be total time played by boys/ number of boys. We can assume each boy plays the same amount of time. This makes it easier, rather than thinking each boy plays a different amount of time.

A way to find this would be to find all possible groupings of 3 among the 4 boys. Then we know how many rounds they played and we can divide by 2 hours to find how long 1 round was. Looking at the groupings we made we see how many rounds each boy plays in order to find the amount of time each of them played. Hoe this helps!

Hope this helps.