You can
put this solution on YOUR website!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
