How do I group items to make the most money?

[Orichi-Esala]

I've been having trouble with my stocks, so I want to make a combo to sell them fast and get more traffic. But when I group them together, I see that the prices are not the same as the average prices. I also have one problem: the amount is different. How can I group them better and faster? Right now I have to do calculations in an Excel sheet, and it takes a long time.