conversations.from: human
conversations.value: Marianne was 20 years old when Bella was 8 years old. How old will Marianne be when Bella turns 18?
conversations.from: assistant
conversations.value: Marianne is 20 - 8 = 12 years older than Bella.
  Bella will turn 18 in 18 - 8 = 10 years.
  So, Marianne will be 20 + 10 = 30 years old then.