Add 15 to the numerator of (3/5), how much should be added to the denominator to keep the size of the fraction unchanged.
把(3/5)的分子加上15，要使分数的大小不变，分母应加上多少．
<gadget id="calculator">5 * 6</gadget>
<output>30</output>

<gadget id="calculator">30 - 5</gadget>
<output>25</output>

<result>25</result>