Are you smarter than a fifth grader!

This is a real 5th grade math problem.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?


Are you smarter than a fifth grader? ;)