conversations.from: human
conversations.value: Jefferson hires a carriage to go to the church.  It is 20 miles away.  The horse can go 10 miles per hour.  It cost $30 per hour plus a flat fee of $20.  How much did he pay for the carriage?
conversations.from: assistant
conversations.value: He paid for 20/10=2 hours
  That means the hourly fee was 30*2=$60
  So the total cost was 60+20=$80