Multiply the numerator of (3/4) by 3, how much should be added to the denominator to keep the size of the fraction unchanged.
把(3/4)的分子乘3，要使分数的大小不变，分母应当加上多少．
<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<gadget id="calculator">12 - 4</gadget>
<output>8</output>

<result>8</result>