The latter term of 6:7 is enlarged by 3 times. To keep the ratio unchanged, how much should be added to the former term.
6：7的后项扩大3倍，要使比值不变，前项应加上多少．
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<gadget id="calculator">18 - 6</gadget>
<output>12</output>

<result>12</result>