An old-fashioned wall clock strikes 5 times at 5:00 p.m. and takes 12 seconds. How many seconds does it take to strike 3 times at 3:00 p.m.?
一个老式的挂钟，在下午5时敲了5下，用时12秒，那么在下午3时敲了3下，用时多少秒．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

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

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

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

<result>6</result>