The clock strikes 4 times at 4 o'clock, and it takes 12 seconds to finish. Then knock 6 times at 6 o'clock, how many seconds did it take to finish knocking.
时钟4点钟敲4下，用了12秒敲完．那么6点钟敲6下，用了多少秒敲完．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">12 / 3</gadget>
<output>4</output>

<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<result>20</result>