Answer:
well, ill put this in short.
if the elevation of the south poles surface is 1.7 miles from sea level, and at sea level from there, is 3,949 miles from the core of the earth, you will need to first see how far away each sea level if from each other:
3,949^2 = 7898 miles from sea level to sea level, and then you have to take into account that the surface from the south pole is 1.7 miles from sea level so, if you add both together you get : 7899.7 miles
Answer: 7899.7 Miles from the surface of the south pole to the sea level of the north pole
Hope that this helped!