How can I add custom calculations to my product page?

Store Design
1

Hi. I am working on a project using a custom theme, and I need some product page help. Basically, I need to add the following functionality which does not currently exist (nor is it provided by any apps to my knowledge):

  1. Need to show the price with a per unit designation (as shown in the attached image)

  2. Need to have “Order by Area” calculation and “Order by Pallet” calculation

  3. The results of the calculation need to be able to ADD to the quantity

I have attached a screenshot of a store that does this, so I know it’s possible!