The denominator of (7/9) is increased by 18, how much should the numerator be increased to keep the fraction size constant
(7/9)的分母增加18，要使分数大小不变，分子应增加多少
<gadget id="calculator">7 * 3</gadget>
<output>21</output>

<gadget id="calculator">21 - 7</gadget>
<output>14</output>

<result>14</result>