Xiao Ming is running along the railway at a speed of 3 meters per second. A 150-meter-long train is coming towards him. Its speed is 12 meters per second. How many seconds does it take for the train to pass by Xiao Ming?
小明以每秒3米的速度沿着铁路跑步，迎面开来一列长150米的火车，它的行驶速度是每秒12米，火车经过小明身旁需要多少秒？
<gadget id="calculator">18 + 3</gadget>
<output>21</output>

<gadget id="calculator">147 / 21</gadget>
<output>7</output>

<result>7</result>