Link between EKPO and EBET

Hi

I have tried for long time to find the connection between EKPO and EKBE, but can't find a uniq way.

As example:

EKPO contain 2 lines (2 items)

EKBE contain 3 lines (2 lines for item 00010 and 1 line for item 00020).

The BELNR in EKBE has the same value for 2 of the entries (item 00010 and 00020), but another BELNR for the last item (00010).

Further more the field BUZEI is different.

EBELN EBELP ZEKKN VGABE GJAHR BELNR BUZEI BEWTP

4500002152 00010 00 1 2009 5000000689 0001 E

4500002152 00010 00 1 2009 5000000691 0001 E

4500002152 00020 00 1 2009 5000000691 0002 E

The value that I want from EKBE is EKBE-BEWTP

Any ideas how to get the right line from EKBE?

thanks,