If 6 is added to the denominator of (2/3), how much should be added to the numerator to keep the size of the fraction unchanged?
如果(2/3)的分母加上6，要使分数的大小不变，分子应该加上多少
<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<gadget id="calculator">9 / 3</gadget>
<output>3</output>

<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">6 - 2</gadget>
<output>4</output>

<result>4</result>