The numerator of (5/6) is enlarged by 3 times, how much should be added to the denominator to keep the fraction value unchanged.
(5/6)的分子扩大3倍，要使分数值不变，分母应加上多少．
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<gadget id="calculator">18 - 6</gadget>
<output>12</output>

<result>12</result>