John sublets his apartment to 3 people who each pay $400 per month.  He rents the apartment for $900 a month.  How much profit does he make in a year?
He gets 3*$400=$
<gadget id="calculator">3*400</gadget>
<output>1_200</output>
1200 per month.
So he gets 1200*12=$
<gadget id="calculator">1200*12</gadget>
<output>14_400</output>
14,400 per year.
So he pays 12*900=$
<gadget id="calculator">12*900</gadget>
<output>10_800</output>
10800 a year.
That means his profit is 14400-10800=$
<gadget id="calculator">14400-10800</gadget>
<output>3_600</output>
3600 per year.

<result>3_600</result>