When a 757 passenger jet begins its descent to the Ronald Reagan National Airport in Washington, D. C., it is 3900 feet from the ground. Its angle of descent is 6º. What is the plane's ground distance to the airport?

37,106 ft or 7.03 miles

Step-by-step explanation:

The tangent function relates the angle to the adjacent and opposite sides in the right triangle that models this geometry.

tan (6°) = (altitude) / (ground distance)

ground distance = altitude/tan (6°) = 3900 ft/0.105104 ≈ 37,106 ft

The ground distance to the airport is about 37,106 feet, or 7.03 miles.