Problem in new query creation

Hi Experts,

In a report there are two InfoObjects posting date and Expiry Date. User will enter the posting date at the run time. Now user wants to see the sales values for the conditions as below:-

0<=|(Expiry Date-Billing Date)/30|<6

6<|(Expiry Date-Billing Date)/30|<=12

12<|(Expiry Date-Billing Date)/30|<=18

18<|(Expiry Date-Billing Date)/30|<=24

24<|(Expiry Date-Billing Date)/30|<=36

36<|(Expiry Date-Billing Date)/30|<=48

48<|(Expiry Date-Billing Date)/30|<=60

Now question is when restricting the Expiry Date how to use value of Billing date. For example, say user gives Billing date=x. Now how to give restriction on Expiry date as x <(Expiry date)< x + 30*6.

Any input will be highly appreciated.

Thanks in advance.

Regards,

Prakash