Add 6 to the numerator of (3/10), how much should be added to the denominator to keep the size of the fraction unchanged.
(3/10)的分子加上6，要使分数大小不变，分母应加多少．
<gadget id="calculator">6 + 3</gadget>
<output>9</output>

<gadget id="calculator">9 / 3</gadget>
<output>3</output>

<gadget id="calculator">10 * 3</gadget>
<output>30</output>

<gadget id="calculator">30 - 10</gadget>
<output>20</output>

<result>20</result>