keeping a bank total

[grentech]

i want to be able to keep a running total of a bank account with buying a selling. i have attached my spreadsheet which is half working. the bank balances need to minus the buy price each day but on the day where it has sold it needs to add that to the balance. plus the brokerage needs to be taken out of each both the buy and sell.

so on 100701 i have bought 2086 so that needs to be minused from the bank total of starting at zero.

then on the 100708 2198 needs to be misused but also because there are 2 dates where it is best to sell 2189 and 2190 need to be added.

im not quite sure how to do this