Add 4 to the numerator of the fraction (4/5), how much should be added to the denominator to keep the size of the fraction unchanged.
分数(4/5)的分子加上4，要使分数的大小不变，分母应加多少．
<gadget id="calculator">5 * 2</gadget>
<output>10</output>

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

<result>5</result>