(3/4) Add 12 to the numerator, how much should be added to the denominator to keep the size of the fraction unchanged
(3/4)把的分子加上12，要使分数的大小不变，分母应加多少
<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<result>16</result>