Add 2 to the numerator of (1/9), how much should be added to the denominator to keep the size of this fraction constant.
(1/9)的分子加上2，要使这个分数的大小不变，分母应加上多少．
<gadget id="calculator">1 + 2</gadget>
<output>3</output>

<gadget id="calculator">3 / 1</gadget>
<output>3</output>

<gadget id="calculator">3 * 9</gadget>
<output>27</output>

<gadget id="calculator">27 - 9</gadget>
<output>18</output>

<result>18</result>