Johnny took his allowance of $20 and added an extra $10 to it.  He then invested this sum of money, which tripled in a year.  How much money did he have after a year?
Johnny invested twenty and ten dollars for a total of 20+10=
<gadget id="calculator">20+10</gadget>
<output>30</output>
30 dollars invested.
Johnny tripled this amount of money over the year, for a total of 30*=90 dollars.

<result>90</result>