InfoPath Dev

I am drafting a from which helps me prepare a product formulation. 1. I have a drop down list where I select the product which lists data from an external datasource (SQL) 2. The datasource has a hierarchy structure (parentname/componentname) 3. When I select product (parentname), I get a listbox with all the component names and respective quantities measures. 4. These quantitie measures are per KG What I am trying to achieve is to get a calculated list box where I enter "Total KG required" and get my desired calculated output for all the component names/quantities etc. I suspect that my solution above may not be possible. If it is, I would love to hear your thoughts. Alternative approach to my challenge above would be much appreciated. Thanking you, AR

 Not sure if it's possible with an external data source, yet is your drop list format the same i.e. productname - number KG. if so you might be able to use an inbuilt substring function to extract the number. Then it would be a question of doing the math on that number. Might have to play around so that the extracted item is recognised as a number.