Can anyone answer this question...

This is a 5th grade math problem. If you can open the spreadsheet, you'll see it's a very small list, but growing, of people who have gotten the correct number. This is not a trick question. This is a real math problem so don't say that a bus has no legs. There are 7 girls in a bus. Each girl has 7 backpacks. In each backpack, there are 7 big cats. For every big cat there are 7 little cats.







Question: How many legs are there in the bus?