Math Problem

This math problem has been floating all around the web and emails everywhere, so I thought I would post it. It came to me with an Excel sheet that was password protected, and the answer opened the sheet. Have at it, and leave your answers in the comments. I'll post the answer in a week or so.

QUESTION: 

There is a bus with 7 girls
Each qirl carries 7 bags
Inside each bag there is 7 cats
Every cat has 7 kittens
All cats have 4 legs each

How many legs are in the bus?