not knowing the diameter of the earth:
circumference of a sphere is C=2*PI*r
adding the height of the person the circumference would be 2*PI*(r+6)
wanting the difference between the two you know would have
2*PI(r+6)-2*PI*r
which gets reduced to 12PI
if you need it in power 12 *3.14 = 37.68 = 3.78 x 10^1
depending on the value used for pi answer may be slightly different.