Xiao Ming is walking on the road next to the railway along the direction of the railway. His walking speed is 2 meters per second. At this time, a train comes from behind him. It takes 21 seconds from the front to the rear of the train to pass by him. It is known that all the trains The length is 336 meters, how many meters does the train travel per second?
小明在铁路旁边沿铁路方向的公路上散步，他散步的速度是每秒2米，这时从他后面开过来一列火车，从车头到车尾经过他身旁共用了21秒，已知火车全长336米，求火车每秒行多少米．
<gadget id="calculator">336 / 21</gadget>
<output>16</output>

<gadget id="calculator">16 + 2</gadget>
<output>18</output>

<result>18</result>