conversations.from: human
conversations.value: George was selling some of his old toys on the internet. He managed to sell 3 little cars and a set of Legos. In total, he earned $45. How much did the Legos set cost, if one little car was sold for $5?
  What is the solution?
conversations.from: assistant
conversations.value: George sold 3 cars, so he earned 3 cars * $5/car = $15 from them.
  The lego set cost was then $45 - $15 = $30.