I covered something similar at
https://www.msofficeforums.com/word-...data-list.html. In the case of your document, don't mix form fields and content controls and you may find
Insert Content Control Add-In useful for inserting and editing controls and their lists where appropriate.
It is not clear how you want to create a number based on selections, so I have made an educated guess from which you should be able to derive the required values from three list box controls all of which must have a selected value before the number is revealed. See attached.