Let
be the weight of i-th player.
1. If the mean weight of 4 backfield members on the football team is 221 lb, then

2. If the mean weight of the 7 other players is 202 lb, then

3. From the previous statements you have that

Add these two equalities and then divide by 11:

Answer: the mean weight of the 11-person team is 
Answer: (Attached)
Graphic below is the answer to your question.
you have a 1/6 probability of rolling a 6
so for 3 6's it would be
1/6 x 1/6 x 1/6 = 1/216