a) U = 2 * π * r
<=> r = U / ( 2 * π )
Also:
r ≈ 9,4 * 10 8 / ( 2 * π ) = 1,496 * 10 8 km
b)
U = 2 * pi * r
<=> r = U / ( 2 * π ) = 4 * 107 ( 2 * π ) = 6,366 * 10 6 m
VKugel = ( 4 / 3 ) * π * r 3 = ( 4 / 3 ) * π * ( 6,366 * 10 6 ) 3 = 1,08 * 10 21 m 3
OKugel = 4 * π * r 2 = 4 * π * ( 6,366 * 10 6 ) 2 = 5,09 * 10 14 m 2