Duvidas com formulas / Questions about formulas

Hello I would like help with formulas, I don’t know where to start

I have in my bank, the price of pieces (X) and quantity of pieces (y). I need to find out the billing of each order. For that I need to multiply x * y =z in each record and add it to all the records displayed in the list sector

The way I’ve been doing this is going wrong by multiplying the sum of the entire list by the sum of the value of parts.
I need to do the multiplication between x*y =z first dps add all the z