Multiply the denominator of (4/5) by 4, how much should be added to the numerator, and the size of the fraction remains unchanged.
把(4/5)的分母乘4，分子应加上多少，分数的大小不变．
<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<gadget id="calculator">16 - 4</gadget>
<output>12</output>

<result>12</result>