A 50 meter long train passes over a bridge at the speed of 30 km per hour. If it takes 36 seconds to cross the bridge, what is the length of the bridge?

Answer: Option B

Speed = $$\left(30\times \frac{5}{18}\right)$$  m/sec = $$\frac{25}{3}$$ m/sec
Time = 36 second
Let the length of the bridge be x meters.
Then, $$\frac{50+\text{x}}{36}$$   = $$\frac{25}{3}$$
⇒ 3(50 + x) = 900
⇒ 50 + x = 300
⇒ x = 250 meters