If the clock strikes 3 times at 3 o'clock, it takes 6 seconds to complete, and if the clock strikes 8 times at 8 o'clock, it takes how many seconds to complete it.
时钟3时敲3下，6秒完成，时钟8时敲8下，多少秒完成．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

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

<gadget id="calculator">8 - 1</gadget>
<output>7</output>

<gadget id="calculator">3 * 7</gadget>
<output>21</output>

<result>21</result>