Hello every one i need your help with a formula.

Example

Date Delivered Cost Sold Retail
Price Profit
Pepsi Coke Pepsi Coke Pepsi Coke Pepsi
Coke Pepsi Coke
7/1/08 100 50 1.00 1.15 50 25 1.29
1.39 ???? ????
7/2/08 0 40 15
1.19 1.29 ???? ????
7/3/08 250 70 0.79 .85 60 45 0.99
1.09 ???? ????
7/4/08 0 55 35
1.15 1.25 ???? ????

Every day delivery does not come. Each time cost is different.
Every day i put sold and every day sold price is different.

Now i need a formula that will find profit but it must use the old inventory
first. until old inventory is all gone then start next one. The current
formula i have right now is =(K5-E5)*H5


Please help me out i been working on this for about a month. Thank you very
very much.