Add 8 to the numerator of (4/5), how much should be added to the denominator to keep the size of the fraction unchanged.
(4/5)的分子加上8，要使分数的大小不变，分母应加上多少．
<gadget id="calculator">4 + 8</gadget>
<output>12</output>

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

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">15 - 5</gadget>
<output>10</output>

<result>10</result>