Price Adjustment Rule

 Hi

We would like to create a Adjustment Rule for all the Distrubution centers based on Quantity. as below

Ex:

Bill 1

Item                            Qty

A                                 5

B                                  5

C                                  5

A                                   2                   Free Goods

Bill 2

Item                            Qty

A                                 3

B                                  5

C                                  5

but the condition is the Total billed quantity should be greater or equal to 25.

In the above bill1 each line item is having 5 Qty so we have given 2 Free. Where as in the bill 2 the first line is less than 5 so no free items. So we want to configure the same Free Qty setup. How can it be configured in the system

Thanks