Mark buys a Magic card for $100, which then triples in value.  How much profit would he make selling it?
The value went up to 100*3=$
<gadget id="calculator">100*3</gadget>
<output>300</output>
300.
So he gained 300-100=$
<gadget id="calculator">300-100</gadget>
<output>200</output>
200.

<result>200</result>