Little Debbie Nigra from Pittsburgh writes:
Dear Dr. Science,
I have a question that you may be able to answer.
When I was at the beach with my friends this summer, there was a big ship on the horizon. We were wondering how far out it was, which led us to wonder how far the horizon was. Do you know how far the horizon is on a clear day, if your eyes are infinitely sharp and there's nothing in the way? Am I oversimplifying?
Using reasonable assumptions, can you answer her question? For your information, the Earth can be assumed to have a radius of 4,000 miles. Also, we may assume that little Debbie is exactly 5.280 feet tall.
I give up, show me the solution.