After adding 20 to the denominator of (4/5), how much should be added to the numerator to keep the size of the fraction unchanged.
(4/5)的分母加上20后，要使分数的大小不变，分子应加上多少．
<gadget id="calculator">5 + 20</gadget>
<output>25</output>

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

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

<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<result>16</result>