The solution for this problem is:
v^2 = GM/r
r=GM/v^2
but
velocity = 2pi r / P
so we can say that
r = GM/(2pi r)^2 / P^2
r^3/GM = P^2/(4 pi^2)
r = (P^2 ( GM/(4pi^2)))^(1/3)
P = 5.8h = 5.8x3600s
GM = 6.67 × 10^−11 x 1.9 × 10^27
( (5.8 x 3600)^2 x (6.67e-11 x 1.9e27) / (4 x pi^2) )^(1 / 3) = 111 856 243 m
now subtract 6.99 × 10^7 m, the answer is: = 41956243 m