The numerator of (2/3) is increased by 6, how much should be added to the denominator to keep the size of the original fraction unchanged.
(2/3)的分子增加6，要使原分数的大小不变，分母应加多少．
<gadget id="calculator">3 * 4</gadget>
<output>12</output>

<gadget id="calculator">12 - 3</gadget>
<output>9</output>

<result>9</result>