Crystal Reports Group Summary formula

Message

   Hi,
I am using CR 9.2. Please help me to form a formula for a group header. When i use 'Insert>Summary', it gives me exact summary of my group. But no option to put a condition by date range. How can i make a conditional sum for a group? I will try to explain it more with an example:

Sugar (Group)  (Summary of below items needed here with condition of date. Eg: 50)
  - Sugar itemA      20
  - Sugar itemB      20
  - Sugar itemC      10

Tea (group)      (Summary of below items needed here with condition of date. Eg:40)
  - Tea itemA          10
  - Tea itemB           10
  - Tea itemC           20

Thanks for your help..