Add 7 to the numerator of (7/18), how much should be added to the denominator to keep the original fraction value unchanged.
(7/18)的分子加上7，要使原分数值不变，分母应加上多少．
<gadget id="calculator">7 + 7</gadget>
<output>14</output>

<gadget id="calculator">14 / 7</gadget>
<output>2</output>

<gadget id="calculator">18 * 2</gadget>
<output>36</output>

<gadget id="calculator">36 - 18</gadget>
<output>18</output>

<result>18</result>