Leg Math

This is a 5th grade math problem.

This is not a trick question.

This is a real math problem, so don't say that the bus doesn't have 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.The bus driver is not in the bus at this time.

Question: How many legs are there in the bus?If you think you know the answer post it in a comment. Just post your answer no calclulations please. Let others figure this out on their own. Thanks. No peeking at other's answers first now! Good luck. After one week, I'll post the answer.