Add 5 to the numerator of (5/7), how much should be added to the denominator to keep the fraction value unchanged.
(5/7)的分子加上5，要使分数值不变，分母应加上多少．
<gadget id="calculator">7 * 2</gadget>
<output>14</output>

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

<result>7</result>