I need a help to know how we can fetch or manipulate the dynamically added row values of sub forms to another form.

Form 1 : Products_form

                             Product_Name field

                             Cumulative_Sales_Value field

Form 2: Inventory_Form

                                          Total_Billed_Value field

            Sub Form : SubForm

                                          Billed_Product Field  - (Lookup Field from Product Name Field of Products_form)

                                          Billed_ Price Field

Two requests...

1.  Total_Billed_Value of Form 2 has to be updated with Sum of the SubForm's Billed_Price Columns.

2. Whenever a new row has been added/deleted in the SubForm, Cumulative_Sales field of Form 1 has to be updated for every added rows with reference to Billed_Product.

SubForm will be added a row dynamically. The number of rows may vary. 

Please help here.