Answer: 8
Step-by-step explanation: In order to answer this question you start with the 85 shells that Lilly has in her collection, and then subtract the 13 shells that she gave away. 85 - 13 = 72, meaning that she has 72 shells left. Next, she divides the remaining 72 by 9, which will give you 8 groups. 72 / 9 = 8.