Multiply the denominator of the fraction (6/(x)) by 3, to keep the size of the original fraction unchanged, how much should be added to the numerator
把分数(6/(x))的分母乘以3，要使原分数的大小不变，分子应加上多少
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

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

<result>12</result>