Correct option is (a) 50 m
Let the length of each train be x m.
During crossing, the two trains cover a distance equal to sum of their lengths.
Then, distance covered = 2x m.
Relative speed = 46 − 36 = 10 km/hr
\(= 10 \times \frac 5{18}\)
\(=\frac {25}9\) m/sec
Speed = \(\frac{\text{Distance}}{\text{Time}}\)
⇒ \(\frac{25}9 = \frac{2x}{36}\)
⇒ x = 50
Hence, the length of each train is 50 m.