Add 24 to the denominator of (7/12), how much should be added to the numerator to keep the fraction value unchanged.
(7/12)的分母加上24，要使分数值不变，分子要加上多少．
<gadget id="calculator">12 + 24</gadget>
<output>36</output>

<gadget id="calculator">36 / 12</gadget>
<output>3</output>

<gadget id="calculator">7 * 3</gadget>
<output>21</output>

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

<result>14</result>