Final answer:
To find out how many shells Brian has left, subtract the shells given to Abigail and Cooper from the total number of shells he found. Brian has 95 shells left.
Step-by-step explanation:
To find out how many shells Brian has left, we need to subtract the number of shells he gave to Abigail and Cooper from the total number of shells he found.
First, subtract the shells given to Abigail (187) from the total shells (486): 486 - 187 = 299 shells.
Then, subtract the shells given to Cooper (204) from the previous result: 299 - 204 = 95 shells.
Therefore, Brian has 95 shells left.