How do I update data in 3 related files in Excel?
 

I have file A which content of Price List. All the items in the File A is
calculated in other Calculation files which named according to the names of
the items (ex.File B), so there are lots of files B. Every File B is a
calculation of materials which related to File C which consist of the
Material Price list.
Usually the sequence is : When I made changes in File C, then I have to open
each of file B so the calculation can be automatically updated. And then I
opened File A so excel can update the price list.
It seems that excel will only automatically update data if we open the file.
What I want to do now is : When I change any material price in File C, then
I wish excel will automatically update the value in File A, without having to
open each of File B, because there are hundreds of File B.
How to do that? Thank you very much.