When the clock strikes 4 times at 4 o'clock, it takes 12 seconds to finish knocking, and it knocks 8 times at 8 o'clock, how many seconds to finish knocking.
时钟4点敲4下，12秒敲完，8点敲8下，多少秒敲完．
<gadget id="calculator">8 - 1</gadget>
<output>7</output>

<gadget id="calculator">7 * 4</gadget>
<output>28</output>

<result>28</result>