conversations.from: human
conversations.value: I would love to understand how to solve this problem: Deborah has four letters to mail. Standard postage is $1.08 per letter, with an additional charge for international mail. Deborah is mailing two letters internationally, and she is paying $4.60 to mail four letters. How many cents is the additional charge per letter for international shipping?
  Can you explain?
conversations.from: assistant
conversations.value: A dollar is 100 cents, so standard postage is 108 cents.
  Deborah’s four letters cost 108 * 4 = 432 cents for standard postage.
  She paid 460 - 432 = 28 cents for international shipping on two letters.
  Thus, the additional international shipping charge is 28 / 2 = 14 cents per letter.