Add 12 to the numerator of (4/9), what should be the denominator to keep the size of the fraction constant?
(4/9)的分子加上12，要使分数的大小不变，分母应该多少．
<gadget id="calculator">12 + 4</gadget>
<output>16</output>

<gadget id="calculator">16 / 4</gadget>
<output>4</output>

<result>4</result>