The clock strikes 3 times at 3 o'clock, and the knocking is over in 6 seconds. How many seconds does it take to knock 9 times at 9 o'clock?
时钟3时敲3下，6秒敲完．9时敲9下，需要多少秒．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">9 - 1</gadget>
<output>8</output>

<gadget id="calculator">3 * 8</gadget>
<output>24</output>

<result>24</result>