Hi,
in your version there is included the plugin "statFunctions" (maybe you have to activate it).
Unfortunately you didn't answer all questions at the beginning.
With this you count the number of selected seats.
As there is no subquestion relevance on single punch questions you have to use a hidden multiple question where you preset the still available options by an equation, and set the array filter of your single question on this multiple.
If you are able to read German or to use Google translate:
In the German part of the forum (page 6,7,or
you find my "Tutorial 3: Gimmicks..." where this is shown (with some sample surveys)
Joffm