(2/3)=((2+())/12).
(2/3)=((2+())/12)．
<gadget id="calculator">12 / 3</gadget>
<output>4</output>

<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<gadget id="calculator">8 - 2</gadget>
<output>6</output>

<result>6</result>