fraction is (3/5), if 9 is added to its numerator, how much should be added to the denominator to keep the size of the fraction unchanged?
一个分数是(3/5)，如果将它的分子加上9，要使这个分数的大小不变，分母应该加上多少？
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

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

<result>15</result>