conversations.from: human
conversations.value: A jar contains 9 blue pens, 21 black pens, and 6 red pens. Four blue pens are removed and then seven black pens are removed. How many pens are left in the jar?
conversations.from: assistant
conversations.value: There are 9-4 = 5 blue pens left in the jar.
  There are 21-7 = 14 black pens left in the jar.
  There are 5+14+6 = 25 pens left in the jar.