I've checked out your c3p file, and I think the issue is due to the fact that you're actually hardcoding all levels from 1 to 10 by copying the logic.
I really wouldn't do that. I would make the level a variable and make functions that do the logic based on the variable. Only one set of logic instead of 10 times the same. Also, you could use dictionaries or arrays instead of txt files or you could alternatively make up the question using randomisation. For example: in the 1st level you would generate numbers between 1 and 10 and solutions between and 15. In level 2 generate numbers between 10 and 20 and solutions between 10 and 30. Something like that.
If you want some inspiration on creating apps you can check out my youtube channel.
There is no template for a quiz (yet) but you can see similar solutions for example
for sudoku : youtu.be/Rq0iQGcVQtc
for a logo quiz: youtu.be/rDKwhBwf7Ck
Hope that helps you in some way.