Add 15 to the numerator of (5/9), how much should be added to the denominator to keep the size of the fraction constant
把(5/9)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 + 15</gadget>
<output>20</output>

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

<gadget id="calculator">9 * 4</gadget>
<output>36</output>

<gadget id="calculator">36 - 9</gadget>
<output>27</output>

<result>27</result>