After the denominator of (7/12) is increased by 36, how much should the numerator be added to keep the size of the fraction unchanged?
(7/12)的分母增加36后，要使分数的大小不变，分子应加多少．
<gadget id="calculator">36 + 12</gadget>
<output>48</output>

<gadget id="calculator">48 / 12</gadget>
<output>4</output>

<gadget id="calculator">7 * 4</gadget>
<output>28</output>

<gadget id="calculator">28 - 7</gadget>
<output>21</output>

<result>21</result>