First in First out (FIFO) accounting for equity trade's book cost

Hi,

I have a number of equity trades (both purchase and sales). I need to know the book cost of those sale trades to figure out the realized gain/loss according to First-in-first-out method.

Since the unit sold may included units bought at different time and different price, so I have to first exhaust the first lot that I purchase before moving into second lot, and so on and so for.

Column G - J are for illustration.
I highlighted K10, K11 and K12 are book cost that I want to calculate. Instead of manually separating out units in each lot previously bought. Is there an automatic way? I would not mind adding new columns to ease calculation. Thanks.