Final answer:
The expression that can be used to determine the number of shells each person takes home is (Total number of shells - 8) ÷ 4.
Step-by-step explanation:
To determine the number of shells each person takes home, we can use the expression:
(Total number of shells - 8) ÷ 4
This expression subtracts 8 shells from the total number of shells collected and then divides the remaining shells equally among you and your three friends.
For example, if you collected 20 shells, the expression would be:
(20 - 8) ÷ 4 = 12 ÷ 4 = 3
So, each person would take home 3 shells.