Hi, Need help, Can any body please tell me that how PMAC calculates the item cost

I have created a batch.. Two ingredients are involved for making the product.

Ingredients

CHOCOLATE SYRUP     10.15841(On-Hand balance)

CHOCOLATE WATER     10.15841(On-Hand Balance)

Product

CHOCOLATE FG             24(On-hand balance)

I have created a PO Of the above ingredients of quantity 20(both) at rate of 200.

Then i received the quantity in the same subinventory where the above ingredients are already exists.

Now,the quantity of the both ingredients in the subinventory are 30.15841.

Then i have created a batch in which i gave 15 units of product in product quantity tab(Required).

7.5 units of each ingredients are used to make the above quantity of the product.