conversations.from: human
conversations.value: Eric has 20 marbles. He has 12 white marbles, 6 blue marbles, and the rest are green marbles. How many green marbles does Eric have?
  Solve this problem.
conversations.from: assistant
conversations.value: Eric has a total of 12 + 6 = 18 white and blue marbles.
  Thus, he has 20 - 18 = 2 green marbles.