10-Oct-07 10000 Goog
20-Nov-08 2000 intc
29-Nov-08 4000 intc
21-Nov-09 goog -20000
21-Nov-09 intc -10000

How do I calculate returns for Goog and Intc individually, if I sold on the
21st Nov, and bought on three different dates?

I have a big list of such transactions. I want to calculate returns for
individual stocks.