Lots and Lots of Pussy

Cats that is...

Here is one of those math problems circling the globe.
Post your answer and I'll let you know if you're right since I can attach the magic spreadsheet everyone signs...

Test of your math skills...

You can't get the attached spreadsheet open unless you put in the correct
password. The password happens to be the answer to the math question posed
below. Good luck. Once you get it open, add your name to the bottom and
send to your friends.

This is a 5th grade math problem. If you can open the spreadsheet, you'll
see it's a very small list 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 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? (The number of legs is the password
to unlock the excel spreadsheet. If you open it, add your name, save it,
and then send it on to see who else can unlock it.)