How many kilometers is Neptune away from the sun?
.4 -significant digits (sd ) approximation for the orbital average distance is 4.504 E+09 km.
I have used wiki approximations semi-major axis a = 30.110387 AU and 4-sd eccentricity e = 0.009456.
The average distance s semi-minor axis b = 30.109 AU = 4.504 E+09 km..
1 AU ( b for the Earth ) = 149597870 km.
It is inaccurate to show more sd, in view of e being known as a 4-sd approximation only. More sd in e would yield more sd in the answer.