Billing documents: (Urgent! )

Hi Experts,

Please help me out how to do the following tasks in Billing documents..

1.How to find out the sum of price of all products(materials) sold in a period of time using all types of Billing plans? And also in case if the material/product being complex and the materials are only exploded in the delivery?

What r the tables to be refered?

2.How you can fetch the pricing condition information for an item in a delivery from e.g. the sales order?

Please get me some idea.

Thanks a lot in advance.