Issue in query structures

Hello Guru's,

I have accounts for company codes like beolw

Company Code Account number Balance

1000 9400 1200

1000 5100 1250

1001 9400 2000

1001 5100 1500

1002 9400 3000

for this i need to calculate the items based on group of Account number

Tax( for company1000) = 9400(account number) + 5100 (account number) = 2450( balance)

Tax( For company is 1001) = 9400 = 2000 ( balance)

Tax ( For campany 1002) = 9400 = 3000( balance)

for this requirement i created a Structure in that i created a new selection characteristic with restricting the account number with 9400, 5100 but i get the balances like

Tax( for company1000) = 2450( balance)

Tax( For company is 1001) = 3500 ( balance) ( wrong value)

Tax ( For campany 1002) = 3000( balance)

please help me in this ....

Thanks,

sneha