problem realated finding profit and lose in shop inventory project

There are Two options basically
1 Hire Someone who can work for you.
2 Work Hard Try to Learn some basic programming and with a positive approach Start working.

The main Problem in your question is we don't know how you are saving details and what logics you are using.Calculating Profit or loss is not a big deal and i will suggest you to first write logics like what you have to do and then try to convert them in C# code

// There should be some base value to which you are comparing whether its profit or loss get it
// read the current value for which you want to calculate whether its profit or loss
// compare them and decide whether it is profit or loss