Calculations in a Table

Hi Everyone. I am developing a module in which I will need the learner to look at a price list for an item and then determine the quantity by looking at a floor plan. When the learner enters all the values they click a calculate button and presto, you get a grand total. Yes, I could have put the triggers to fire on the change of focus but that is a lot of triggers. 

But wait, there is more. If the grand total value isn't what I expect it to be (in this case "30") the state changes and the text is red. 

 I was not able to insert a numeric entry into a table. Neither was I able to figure out how to change the state of text in a table. So to over come these challenges, I overlaid the table with numeric entry fields and a standard text box for the Grand Total. 

Finally, I configured the tab order so a learner can easily tab through to enter the values. 

I hope someone else finds this useful. If you need help, feel free to ask, but be ready to send me something like a company tee-shirt or other swag. Seriously, don't make me open a Patreon account. 

What improvements can you make to it? Or suggestion on which for me to work?