Final answer:
The expression that represents the total number of coins Rory has after receiving an additional 8 coins from his aunt is 15c + 8, where c represents the number of coin collections.
Step-by-step explanation:
Rory had a collection with 15 coins each. If we don't know the number of collections, we can call the number of collections c. If Rory's aunt gave him 8 more coins, we want to add that amount to the coins he already has from his collections. The expression for the total number of coins Rory has now is:
15c + 8
This formula multiplies the number of collections by 15, since each collection contains 15 coins, and then adds the 8 coins his aunt gave him.