The numerator of (2/7) is increased by 4, how much should the denominator be increased to keep the size of the fraction constant
(2/7)的分子增加4，要使分数的大小不变，分母应增加多少
<gadget id="calculator">7 * 3</gadget>
<output>21</output>

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

<result>14</result>