regarding inner joins and calculations

Dear Experts,

I have a simple problem but i am a little confused. The problem is that i have 3 tables one is ekpo, ekes,ekbe

from ekpo i have to take matnr value and with respect to the matnr value i have to do this

Field discription is opening stock to get this value i have to do this

FOR ANY material sum of MENGE of EKES minus sum of MENGE of EKBE where VGABE=1

Where EKES. EBELN = EKBE. EBELN And EBELP

For input date range for EKBE BUDAT, EKES EINDT

could you help me out with this problem