Question 95818
when you stand on the deck, your line of sight to the horizon (distance you can see) is tangent to the circumference of the Earth


a radius of the Earth is perpendicular to this tangent ... this radius and your line of sight are 2 sides of a right triangle


the third side (which is the hypotenuse) is a radius of the Earth plus the 100 foot height of the deck


by Pythagoras, x^2+(3960*5280)^2=((3960*5280)+100)^2 ... using a calculator, x is approximately 64667 ft or 12.25 mi