How can I display total square meters per pack on the product page?

I’m looking to add a piece of information next to the quantity selector on the product page, that changes as the customer increases the number of packs in the quantity selector.

Our products have a certain square meter per pack, so as the customer increases the quantities, I wanted to show the total square metres that they would be getting for that amount of packs.

A simple maths code, but I dont know where to get the information for the quantity shown in the quantity selector

Please help

thanks

Why do I never get responses to any of my queries!