Lizzy: James decides to start making his own coffee. He buys a coffee machine for $200 and gets a $20 discount. He figures it will cost him $3 a day to make his coffee. He previously bought 2 coffees a day for $4 each.  How long until the machine pays for itself?.
Me: Hmmm, let me think. I think this is the detailed solution:
User
He bought the machine for $200 - $20 = $180. He used to spend 4 * 2 = $8 a day. So he saves $8 - $3 = $5 a day. So it will take him $180 / $5 = 36 days to pay for itself. Final answer: 36.
Assistant