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-$20=$
<gadget id="calculator">200-20</gadget>
<output>180</output>
180.
He used to spend 4*2=$
<gadget id="calculator">4*2</gadget>
<output>8</output>
8 a day.
So he saves $8-$3=$
<gadget id="calculator">8-3</gadget>
<output>5</output>
5 a day.
So it will take him $180/$5=
<gadget id="calculator">180/5</gadget>
<output>36</output>
36 days to pay for itself.

<result>36</result>