How to get sub total in excel

Hello,
plz help me in getting sub total, for following example

Reg exp

ab01 11
ab01 10
ab01 9 sub total=30
ab02 8
ab02 7
ab02 6 sub total=21
cb01 5
cb01 4
cb01 3 sub total=12
cb02 2
cb02 2 sub total=04


here reg is automatically cumming from report.
i am want automatically sum the exp with respect Reg