Thanks all
I think PMM is right. Below is what I'm understood from the cic guide ( part 1 p26) :
Sponsor, per applicantion : $ 75
Principal applicant who is under 22 y of age and not married : $75
RPRF : $0.00 ( EXEMPTED ) because the principal apllicant is adependent child of the sponsor
Total: $150
pls confirm