Correct Answer: Option D
4.5 km/hr = (4.5 x (5/18)) m/sec
=5 m/sec. = 1.25 m/sec,
and
5.4 km/hr = (5.4 x (5/18)) m/sec
= 3 m/sec = 1.5 m/sec.
Let the speed of the train be x m/sec.
Then, (x - 1.25) x 8.4 = (x - 1.5) x 8.5
=> 8.4x - 10.5 = 8.5x - 12.75
=> 0.1x = 2.25
=> x = 22.5
Therefore, Speed of the train = (22.5 x 18/5) km/hr
= 81 km/hr.
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