Hi John!
Thank you very much for your kind help! It almost worked! The b value (Are we counting participants) is set to NULL. But I realised that the true/false field does not work with the Condition Logic setting (In my field number of participants (b) I have: Show this field if -> Are we counting participants (a) -> Value is equal to -> Checked).
But when checked it does not show field b (number of participants).
Please share your ideas of what I could if possible.
Wish you a great day!
David