Party A and Party B are walking in opposite directions on the sidewalk parallel to the rail, and a train passes by Party A at a uniform speed, which takes 15 seconds.
Suppose the train speed is x km/h, then
15(x+3.6)= 17(x-3.6)
Solution: x=57.6
The train speed is 57.6 km/h,
Therefore, the train length is 15/3600*(x+3.6)=255 meters.