Answer:
v = 7671.57 m/s
T = 1.55 hours 
Step-by-step explanation:
mass of Earth, M = 6 x 10^24 kg 
Radius of earth, R = 6400 km = 6.4 x 10^6 m 
height, h = 400 km 
Velocity is given by 

where, G be the universal gravitational constant. 
G = 6.657 x 10^-11 Nm^2/kg^2 

v = 7671.57 m/s 
Let T b the period 


T = 5566.53 second 
T = 1.55 hours