To show the angle of depression, draw
a horizontal line at the top of the tower:



The angle between that horizontal and the 
line of sight to the boat is 3°



Now by alternate interior angles the angle in the right
corner of the triangle is also 3°



Now 60 is the opposite side to the angle 3° 
at the bottom right corner, and x is the adjacent side.

So we know to use tangent

tan(3°) = 

Multiply both sides by x

x*tan(3°) = 60

x = 

x = 

or about 1145 feet.

Edwin