It takes 4 seconds for the clock to strike 2 times, how many seconds does it take to strike 4 times.
时钟敲2下用4秒，敲4下用多少秒．
<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">4 / 1</gadget>
<output>4</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

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

<result>12</result>