Totals for product codes on multiple sheets

Hi all,
Can you help a 60 year old dinosaur with minimal & self-taught excel knowledge? I need to run a product totals report every month, summarising product sales from about 90 worksheets, each of which is reporting sales of products in a different area. The products are reported by their product code (Column A 'Item no.' on attached example). Although there are 300 product codes in total, each area will have sold a different variety of products (these are food products by the way) , typically about 100 products per area.
I can do a Data Sort and sub total everything, but then still left with multiple rows for every product code which is very laborious to reduce to a single entry, is there a quicker way that I can do this?
Thanks in advance for any suggestions.

Hi
could you please post an xlsx file instead of xls? Thanks

File should now be in xlsx format,
Thanks

If each area has a data sheet with each Product Code 1 to 100 listed, then you can have a summary page that adds each Product Code up rather easily as the cell locations will be the same on each area's sales data sheet.