Let x be the distance between the plane and the airport.
We have,
Angle of depression = 22°
Altitude = 1800 m
Sin 22° = Opposite/Hypotenuse
=> Sin 22° = Altitude/x
=> Sin 22° = 1800/x
=> x × Sin 22° = 1800
=> x = 1800/Sin 22°
=> x = 1800/0.3746065934
=> x = 4805.04089 m