When 9 is added to the numerator of (3/4), to keep the size of the fraction unchanged, the denominator should be. how much to add
当(3/4)的分子加上9后，要使分数大小不变，分母应该．加上多少
<gadget id="calculator">3 + 9</gadget>
<output>12</output>

<result>12</result>