Formula used: Speed = Distance/Time Calculation: Speed of the train = 54 km/hr = 54 × 5/18 = 15 m/sec Length of the train = 270 m Length of the tunnel = 270 m Total distance to be covered is combined length of both trains = 270 + 270 = 540 m ⇒ Time taken by train to cross the tunnel = 540/15 = 36 seconds