conversations.from: human
conversations.value: I need help with this problem:
  Janey has 3 more than twice the number of books that Sally has. If Janey has 21 books, how many does Sally have?
conversations.from: assistant
conversations.value: Let x be the number of books that Sally has
  Janey has 3+2x books
  3+2x=21
  2x=18
  x=9