Add 8 to the numerator of (4/7), how much should be added to the denominator to keep the fraction size constant
(4/7)的分子加上8，要使分数大小不变，分母应该加上多少
<gadget id="calculator">8 + 4</gadget>
<output>12</output>

<gadget id="calculator">12 / 4</gadget>
<output>3</output>

<gadget id="calculator">7 * 3</gadget>
<output>21</output>

<gadget id="calculator">21 - 7</gadget>
<output>14</output>

<result>14</result>