Default choice display option using piped text (subtraction of options)

Hi all! In my questionnaire, I have two items in the following order: 1. How many children do you have in your class: [text entry] 2. An item with the following response scale (Constant Sum type): [respondent types in a number] Never [respondent types in a number] Sometimes [respondent types in a number] Always In the 'Sometimes' option I want to have a number displayed that takes the value from questions 1 (for instance 10 children) which is subtracted by the number entered in the 'never' and 'always' option (for instance, respondent enters 1 in 'Never', 2 in 'Always' and given they entered 10 in the first question, 'Sometimes' option should display 7). Having read some Qualtrics guidelines, I came up with this equation, which doesn't work when I use 'Add Default Choices' and then pipped text option for 'Sometimes': $e{ q://QID2/ChoiceTextEntryValue - q://QID3/ChoiceNumericEntryValue/1 } Could someone please advise me how can this be achieved? Best wishes Nora