(7/9) How much should be added to the denominator to keep the fraction size unchanged by adding 21 to the numerator
(7/9)分子加上21要使分数大小不变分母应加上多少
<gadget id="calculator">7 + 21</gadget>
<output>28</output>

<gadget id="calculator">28 / 7</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>