(3/5)=((3+6)/(5+())).
(3/5)=((3+6)/(5+()))．
<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<gadget id="calculator">9 / 3</gadget>
<output>3</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">15 - 5</gadget>
<output>10</output>

<result>10</result>