The numerator of the fraction ((a)/6) is multiplied by 3, how much should be added to the denominator to keep its size constant
分数((a)/6)的分子乘3，要使它的大小不变，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>