For example I have a data set like this:

2001-2-8 Buy 50
2001-2-7
2001-2-6 Sell 73
2001-2-5 Sell 72
2001-2-4
2001-2-3
2001-2-2
2001-2-1 Buy 19
..........

I have the following questions:
1) What formula do I have to put so that it will only calculate the transaction Profit (or Loss) for the first value from "Sell" after a "Buy"?
2) How do I place a new stop loss or cut profit criteria?
3) Can I count How many trades I made as a result?

Thank you for your help. Its some practice for a text book.