If the numerator of a fraction is enlarged to 4 times its original size (16/5), how much should be added to the denominator so that the size of the fraction remains the same?
一个分数的分子扩大到原来的4倍是(16/5)，分母应加上几，才能使分数的大小不变？
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">20 - 5</gadget>
<output>15</output>

<result>15</result>