conversations.from: human
conversations.value: Mrs. Lacson harvested 80 sweet potatoes. She sold 20 of them to Mrs.  Adams and 15 of them to Mr. Lenon. How many sweet potatoes are not yet sold?
  Work out the solution step by step.
conversations.from: assistant
conversations.value: Mrs. Lacson sold a total of 20 + 15 = 35 sweet potatoes.
  Hence, there are still 80 - 35 = 45 sweet potatoes left unsold.