conversations.from: human
conversations.value: The capacity of Karson's home library is 400 books. If he currently has 120 books, how many more books does he have to buy to make his library 90% full?
  Give me a solution to this problem
conversations.from: assistant
conversations.value: When 90% full, Karson's library holds 90/100*400 = 360 books.
  If he has 120 books in the library now, he needs to buy 360-120 = 240 books to make his library 90% full.