Multiple formulas for multiple sheets

Hello,

I have multiple sheets with sheet 1 as the main sheet for entering data.

A cell for entering a order number

Cells for entering invoice no.'s for each store.
(Which coppies to the rest of the sheets. The above I've figured out with using: =IF(Sheet1!B3="","",Sheet1!B3).

but now I need to know how add total boxes into the main sheet and it automatically adds the number of boxes into the other sheets.