Answer:
Step-by-step explanation: Since there are 7 people who shake hands with everybody including the people who know each other, we can add 11+10+9+8+7+6+5, because each handshake counts once, but the other five can't be counted because they are the people who already know each other and if you add 11+10+9+8+7+6+5, you will also get 16*3 +8 which equals to 56.