Hello,

a)Distance from earth's centre = 6400 + 640=7.04 x 10^6m

Now,

mv^2/r= GMm/r^2

V =   √GM/r  = √56.8 x 10^6

= 7.56 x 10^3 ms ^-1

(B) Total energy after 1500 rounds = Initial energy - Energy loss

= - GMm/2r- 1.42 x 10^5x 1500

=(- 6253-0213) x 10^9

= -6.466 x 10^9J

So, r = - GMm/- 6.466 x 10^9

= 6808 km

Its height above the earth's surface = 6808-6400

= 408 km

(C) Average retarding force, |F |=| dU/dr|

F = Energy loss/Distance

= 1.42 x 10^5/ 2 x 3.14 x 6.924 x 10^3 = 3.3 x 10^-3N

Hope it helps