Radio and TV stations broadcast from high towers. Their signals are picked up by radios and TV’s in houses within a certain radius. Because the Earth is spherical, these signals do not get picked up beyond the point of contact of the near horizontal tangent line as illustrated in the sketch.
What is the maximum broadcasting radius from a radio tower 70m tall? Assume that the circumference of the Earth is 42 650km. Give your answer to the nearest km.