In 2:3, if 6 is added to the latter term, how much should be added to the former term to keep the ratio constant
在2：3中，如果后项加上6，要使比值不变，前项应加上多少
<gadget id="calculator">3 + 6</gadget>
<output>9</output>

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

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

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

<result>4</result>