Add "quantity" to attributes

I would like to add a customized length field with price impact and i want to keep the quantity textfield. This is how i wont it to work: Add a textfield that multiplies the selected attribute and makes impact on the price on the fly. I want the number to be displayed between "Groupname": and "Attrebute" in the cart. I've added some pictures I only need the code then i can implement it myself.