(7/9)=((7+())/27).
(7/9)=((7+())/27)．
<gadget id="calculator">27 / 9</gadget>
<output>3</output>

<gadget id="calculator">7 * 3</gadget>
<output>21</output>

<gadget id="calculator">21 - 7</gadget>
<output>14</output>

<result>14</result>