If the clock strikes several times in the hour, and strikes once every 3 seconds, how many seconds will it strike at 6:00 p.m.
如果时钟在第几小时就敲几下，而且每3秒敲一下，那么下午六点要敲多少秒钟．
<gadget id="calculator">12 + 6</gadget>
<output>18</output>

<gadget id="calculator">18 - 1</gadget>
<output>17</output>

<gadget id="calculator">17 * 3</gadget>
<output>51</output>

<result>51</result>