A 200 meter train takes 15 sec to cross a man who is walking in the same direction at the speed of 4 km/hr. The speed of the train is:

52 km/hr

Let the speed of the train be x km/hr

The relative speed of the train with respect to the man = (x - 6) km/hr

⇒ (x - 4) = $\frac{200}{15}$ × $\frac{18}{5}$ (converting m/s to km/hr by multiplying with x$\frac{18}{5}$)

⇒ (x - 4) = 40 × $\frac{6}{5}$

⇒ x - 4 = 48 

x = 52

Ans = 52 km/hr