A railway worker is standing still under the roadbed. It takes 40 seconds for a train to pass him. If the worker walks in the direction of the train at a speed of 6 kilometers per hour, the train will pass him. It only takes 37.5 seconds to pass, how many kilometers does the train travel per hour?
一个铁路工人在路基下原地不动，一列火车从他身边驶过用了40秒，如果这个工人以每小时6千米的速度迎着火车开来的方向行走，则这列火车从他身边驶过只用37.5秒，则这列火车每小时行多少千米．
<result>90</result>