Usage of "ON" vs "UPON" in English Grammar

Great question! Both "on" and "upon" are correct, but the choice depends on the context and formality of the sentence.

• "On" is more common and used in everyday language. It’s simple and sounds natural in most situations. 
  • Example: I put my backpack on the chair.
• "Upon" is more formal or poetic. It’s often used in literature, stories, or formal writing when you want to sound elegant or old-fashioned. 
  • Example: The knight placed his hand upon the sword.

In your example, "on" is better if you’re writing for everyday communication, like in a school story or casual setting. "Upon" could be used if Emily is writing something formal or dramatic. Thank you and hope this helps!