Answer:
42400 km
Step-by-step explanation:
The time taken by a satellite to complete one revolution around the earth is called the time period of the satellite.
The time period for the satellite is given by

where, R be the radius of earth, h be the height of satellite from earth's surface and g be the acceleration due to gravity.
Substitute, 86400 s for T, 6400000 m for R and 9.8 m/s^2 for g , we get

h = 35954355.13 m
h = 36 x 10^3 km
Distance from the centre of earth is R + h = 6400 km + 36000 km = 42400 km .