Add 4 to the numerator of (2/10), how much should be added to the denominator to keep the size of the fraction constant
(2/10)的分子加上4，要使分数的大小不变，分母应加上多少
<gadget id="calculator">2 + 4</gadget>
<output>6</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">10 * 3</gadget>
<output>30</output>

<gadget id="calculator">30 - 10</gadget>
<output>20</output>

<result>20</result>