Show a math column on the worksheet

Hello, I have a question I want to show a mathematical column in my spreadsheet what it does is that it multiplies the quantity of the product x the price, but he tried several methods so that this multiplication is shown as the total to pay, but I cannot choose the column and show the desired value, I could be very grateful if someone provide me a solution or an idea :frowning_face:

What have you tried so far? Do you have any screenshots to better describe your problem?