conversations.from: human
conversations.value: Lisa, Jack, and Tommy earned $60 from washing cars all week. However, half of the $60 was earned by Lisa. Tommy earned half of what Lisa earned. How much more money did Lisa earn than Tommy?
  What is the solution?
conversations.from: assistant
conversations.value: Lisa earned $60 * 1/2 = $30.
  Tommy earned $30 * 1/2 = $15.
  Lisa earned $30 - $15 = $15 more than Tommy.