conversations.from: human
conversations.value: To make a call from a payphone, you must pay $0.25 for each minute of your call. After 16 minutes, that price drops to $0.2 per minute. How much would a 36-minute call cost?
  Give me a solution to this problem
conversations.from: assistant
conversations.value: First 16 minutes would be a cost of 16 * 0.25 = $4.
  After that, there are 36 - 16 = 20 minutes of the call left.
  And these 20 minutes cost 20 * 0.2 = $4.
  So in total, the 36-minute call would cost 4 + 4 = $8.