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Solution.
The train which is 120 metres in length crosses a pole in 12 seconds implies it is covering the distance 120 metres in 12 seconds.
So speed of this train is 120/12 = 10 m/s.
It is crossing another train traveling in opposite direction in 8 seconds.
Let the speed of this train be y.
It's length is also 120 metres.
So (120+120)/(10+y) = 8.
Or 10+y = 30.
Or y = 20 m/s or 20*18/5 km/hr = 72 km/hr
The correct answer is C.
