Correct Answer - Option 3 : 200 m

Given:

Length of train = 400 m

Speed of train = 60 km/h

Time to cross the bridge = 36 seconds

Formula used:

Speed = (Length of train + Length of bridge)/Time to cross the bridge

1 km/hr = 5/18 m/s

Calculations:

Let the length of bridge be x.

Speed = (Length of train + Length of bridge)/Time to cross the bridge

⇒ (60 × 5/18) = (400 + x)/36

⇒ 600 = 400 + x

⇒ x = 200 m

∴ The length of bridge is 200 m.