conversations.from: human
conversations.value: Break down this math problem: A book costs $4 more than a CD. The CD is 30% cheaper than a $20 album. How much does the book cost?
conversations.from: assistant
conversations.value: The CD is 30/100 * 20 = $6 cheaper than the album.
  So the cost of the CD is 20 - 6 = $14.
  The book is $4 more expensive than the CD, which means it cost 14 + 4 = $18.