InfoPath Dev

hi all, I have a field called Request Number: and the same request number i am displaying inside the repeating repeating table.The original request number is generating automatically. I want implement some like this: If the header request number is REQ0001....when any item inserted in the repeating table this should be genereting like REQ0001/1, if second item inserted it should be like REQ0001/2...it should increment by /1...for your better understanding i have attached the sample template....How can i implement this..your help is appreciated.

I'd use a concat formula and preceding-sibling. Sample attached, save it locally, right click and select design to open in design mode.