a)
For the first 3 spots you have to select 3 boys from 5 and understand that the order amongst those 3 matters so it's 5P3, then for the remaining 6 people it's just 6!
(5P3)*6!
b)
First you select 2 girls from 4, so that's 4C2, you form that with John to make one group, also multiply that...