Add 9 to the numerator of (3/10), how much should be added to the denominator to keep the size of the fraction constant
(3/10)的分子加上9，要使分数的大小不变，分母应加上多少
<gadget id="calculator">3 + 9</gadget>
<output>12</output>

<gadget id="calculator">12 / 3</gadget>
<output>4</output>

<gadget id="calculator">4 * 10</gadget>
<output>40</output>

<gadget id="calculator">40 - 10</gadget>
<output>30</output>

<result>30</result>