value linked to a specific radio selection

Hi!
I do have to calculate a fee.
the fee varies according to the choosen plan : individual (25$) or familial (45$).
thus, i have a radio button with those 2 plans :
[radio radio-953 use_label_element default:1 “Individuel” “Familial”]
but i need to link a fee to each plan.
which i cannot achieve !
What i tried : add a hidden text field (fee = 25)
then use a conditional familial group with hidden text (fee=45)
but even if individual is choosen the fee happens to = 45 anyway.
Thus cf7 doesn’t show the conditionnal group but read the code anyway and apply the according fee.
Is there a way to achieve what i need ?
Thank you and sorry for my english i am french native !
Eric

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