If it takes 4 seconds for the clock to strike twice at two o'clock, how many seconds will it take for the clock to strike six times at six o'clock?
时钟两时敲两下需要4秒，当时钟六时敲6下需要多少秒．
<gadget id="calculator">6 - 1</gadget>
<output>5</output>

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

<result>20</result>