probability

Q18
A letter is known to have come either from London or Clifton. On the postmark only two Consecutive
letters 'on' are legible, What is the chance that it came from London?
ans 12/17


@SanketBiradar
i didnt understand 2/5
can you explain it

@NishantThakre
2 ON are there and in total 5ways consecutive letters can be selected