Add 4 to the numerator of (2/9), how much should be added to the denominator if the size of the fraction is to remain the same
(2/9)的分子加上4，如果要使这个分数的大小不变，分母应该加上多少
<gadget id="calculator">9 * 3</gadget>
<output>27</output>

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

<result>18</result>