Explanation

First, find the speed of the train past the telegraph post:

Speed = Distance / Time = (Length of train) / 8 seconds

Since the length of the train is not given, let's call it "x". Then, Speed = x / 8

Now, find the speed of the train past the bridge:

Speed = Distance / Time = (Length of train + Length of bridge) / 20 seconds

= (x + 264) / 20

Since the speed of the train is the same in both cases, set up an equation:

x / 8 = (x + 264) / 20

Cross-multiply and solve for x:

20x = 8x + 2112

12x = 2112

x = 176

So, the length of the train is 176 meters.

Now, find the speed of the train:

Speed = x / 8 = 176 / 8 = 22 meters/second

Convert the speed to km/hr:

Speed = 22 m/s x (3600 s/h) / (1000 m/km) = 79.2 km/hr

The correct answer is:

79.2 km/hr