Stretch movieclip affecting other movieclip


got a big fixed dimension boxe that have 9 small child boxes positionned like this:

1 2 3

The big boxe is 300x300 and each small boxe are 100x100.

What I need to do is that, if I stretch boxe #1 to 150x150, boxes #2 should become 50x100 so the big boxe remain the same… hope I’m clear enough.

So, how can I do this dynamically hasving in mind that the big boxe can contain unlimited numbers of small boxe?

I just need a startnig point to figured out how to acheive this in AS3,