The distance D, in miles, to the horizon from an observer's point of view over water or "flat" earth is given below, where H is the height of the point of view, in feet. If a person whose eyes are 3 ft above ground level is standing at the top of a hill 69 ft above "flat" earth, approximately how far to the horizon will she be able to see?

10.39 miles

Step-by-step explanation:

The distance to the horizon depends almost completely on the height above sea-level that the observer is looking from. 

Given that  person eyes are 3 ft above ground level and standing at the top of a hill 69 ft above "flat" earth.

Local elevation = 69 ft

Height H of the eye = 69 + 3 = 72 ft

Distance of the horizon in miles = sqrt root (1.5 × height of the eyes in ft)

Distance = sqrt root (1.5 × 72)

Distance = 10.39 miles.