Thank you for your responses to this problem. Particularly good explanations were sent from Danny who goes to High Ash School, Shubha from Northveil Elementary and Abhijit from Bhavans School. Danny said:
Shubha gave a little bit more detail:
(The first train you mention, Shubha, has already been made by Katie in the question, so there are four others as Danny concluded.) Well done to you all.