(2/(b)) Add 2b to the denominator, how much should be added to the numerator to keep the fraction size unchanged?
(2/(b))分母加上2b，要使分数大小不变，分子要加上多少
<gadget id="calculator">2 * 3</gadget>
<output>6</output>

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

<result>4</result>