conversations.from: human
conversations.value: Thomas has 25 drawings to display. 14 of the drawings were made using colored pencils. 7 of the drawings were made using blending markers. The rest of the drawings were made with charcoal. How many are charcoal drawings?
conversations.from: assistant
conversations.value: Thomas made 14 + 7 = 21 colored pencil and blending marker drawings.
  Thomas made 25 total drawings – 21 colored pencil and blending marker drawings = 4 charcoal drawings.