If the denominator of (2/5) is increased by 15, how many times should the numerator be enlarged to keep the size of the fraction constant?
(2/5)的分母增加15，要使分数的大小不变，分子应扩大多少倍．
<gadget id="calculator">5 + 15</gadget>
<output>20</output>

<gadget id="calculator">20 / 5</gadget>
<output>4</output>

<result>4</result>