In 6:7=12:14, if 7 is changed to 21, how much should 6 be changed to, and this ratio still holds true.
在6：7=12：14中，如果把7改成21，那么6应改成多少，这个比例式仍然成立．
<gadget id="calculator">21 / 7</gadget>
<output>3</output>

<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<result>18</result>