I am taking the same class online and after searching for several days found
this formula d=7.14 times the sqrt of (1.33*height of tower).
d is measured in Km.
for a 100m tower it would be
sqrt(1.33*100)*7.14, sqrt(133)*7.14, 11.53*7.14 = 82.32Km.

My problem is I forgot that I need to find the average height of a tower
so I can add 10m to it.