The former term of 12:7 is doubled, how much should be added to the latter term to keep the ratio constant
12：7的前项扩大2倍，要使比值不变，后项应加上多少
<gadget id="calculator">7 * 2</gadget>
<output>14</output>

<gadget id="calculator">14 - 7</gadget>
<output>7</output>

<result>7</result>