Create coded list in excel

Hello my most humble computer users,

I have a hard one here...And I think it will be harder to explane...
I have an excel file that has a several destinations with a unique code (e.g. Dest-aa, Dest-bb, Dest-cc..) and several zones (e.g. A,B,C) and for each of the zones I have to create a serial number for each group to mail merge onto the letter...for example zone A, Destination aa requires 20 passes (A-aa-1, A-aa-2 and so on to 20) then 35 for zone B (B-aa-1...B-aa-35)
The Excel file kinda looks like:
Zone Dest-aa Dest-bb Dest-cc
A----- 20------ 35------ 54
B----- 52------ 45------ 47
C -----75 ------54------ 58
How Can I do this?

Thank you for your valuable time,

Love and respect
Sak01