Condition calculated based on the percentage of the quantity of the item

Greetings and Happy 2015 to all

I would like your help in the following case ... need to create a condition Zxxx in percentage and in the calculation scheme is calculated on the basis of the quantity of the item, ie the value of the condition is calculated based on the percentage of the quantity of the item.

The other case that would greatly your help is as follows:

having the following variables

- NV = Net value = 3000 USD

- Qty = quantity of the item

- UN = unit price

- Zxxx = Condition Zxxx

- % = 4.27%

How could apply in calculation scheme of the price for Zxxx through the following formula Zxxx = (NV / UN) * %

Any Help Please.