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?
He bought the machine for $200-$20=$<<200-20=180>>180
He used to spend 4*2=$<<4*2=8>>8 a day
So he saves $8-$3=$<<8-3=5>>5 a day
So it will take him $180/$5=<<180/5=36>>36 days to pay for itself
#### 36