Answer: 
The 60 cans of dog food they require to feed 8 puppies for 6 days 
Explanation: 
The loving puppy pet store needs: 40 cans to feed 16 puppies for 2 days 
Let's Divide by 2: 20 cans to feed 16 puppies for 1 day 
Let's Divide by 2: 10 cans to feed 8 puppies for 1 day 
Let's Multiply by 6: 60 cans of dog food to feed 8 puppies for 6 days 
So 60 cans of dog food need to feed 8 puppies for 6 days.