Speed of train in m/sec = 72 km/hr x 5/18 = 20 m/sec
Distance covered in meter = Time taken in crossing the platform in sec x speed in meter = 30 sec x 20 m/sec = 600m
Now, we know , Distance covered by train in crossing the platform = Length of train + Length of Platform
Therefore, length of the train = 600m - 400m = 200m
