Add 6 to the numerator of (2/7), how much should be added to the denominator to keep the fraction value unchanged
把(2/7)的分子加6，要使分数值不变，分母应加多少
<gadget id="calculator">7 * 4</gadget>
<output>28</output>

<gadget id="calculator">28 - 7</gadget>
<output>21</output>

<result>21</result>