In 3:2, if the former term is enlarged by 3 times, how much should be added to the latter term to keep the ratio constant.
在3：2中，如果前项扩大3倍，要使比值不变，后项要加上多少．
<gadget id="calculator">2 * 3</gadget>
<output>6</output>

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

<result>4</result>