A clock strikes 3 times at 3 o'clock, and 6 times at 6 seconds, how many seconds to finish.
一个时钟3点钟敲3下，6秒种敲6下，多少秒钟敲完．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

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

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

<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<result>15</result>