Answer:
Step-by-step explanation: If Nina fills 10 bags, each with 3 treats, she would have a total of 30 treats (10 bags x 3 treats per bag). If she fills 20 bags, she would have 60 treats (20 bags x 3 treats per bag). If she fills 30 bags, she would have 90 treats (30 bags x 3 treats per bag). Since she only has 78 treats, she can fill between 10 and 20 bags, but not more than 20 bags.
If she fills 10 bags, she would use 30 treats, leaving her with 48 treats. If she fills 11 bags, she would use 33 treats, leaving her with 45 treats, which is not enough to fill another bag. Therefore, she can fill fewer than 11 bags, but not more than 20 bags.