you can use the switch command in the Trigger after update of your choice field. Since I don't know anything about your DB, I'm going to make field names up. Please replace with your own.

switch choicefield do
case 1:
fees := 15
case 2:
fees := 40
end

I only did the first two since you said:

Salman said:
and the third will be 0 $

There is no built in "note" capability, so you will have to create a multiline text field and call it "note". You can put in the Display field only if part of the note field to say choicefield = 4 so it will only show when choice 4 is selected.