Add 6 to the numerator of (3/7), how much should be added to the denominator to keep the size of the fraction unchanged.
(3/7)的分子加上6，要使分数的大小不变，分母应加上多少．
<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<gadget id="calculator">9 / 3</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>