here is ur solution:-
Angle of rain, a = 30 degrees
when the man runs with the speed of 10 km/h he finds that rain falls verically that means that the horizontal component of rain was 10 km/h.
Vx = 10 km/h
thus now vertical comppnent of rain is, Vy:
Vx/Vy = tan 30
Vy = 17.32 km/h