Solve the Integral in cylindrical coordinates
∫∫∫ dxdydz/(sqrt( x^2 + y^2 + (h-z)^2)
Where B is the Ball with a Radius R around (0,0,0), and the parameter h is greater than R.
And then infer the average on that ball B with radius R of the distance opposite to the point (0,0,h)
(the average of function f on some shape v is defined as
[ ∫∫∫ f(x,y,z) dxdydz ] / vol V