Let the building height be 78 m, the tower height be h m, and the horizontal distance between them be d m.
The angle of depression to the bottom of the tower is 45°.
The angle of depression to the top of the tower is 30°.
For the angle of depression to the bottom of the tower:
tan(45°)=d78
1=d78
d=78 m
For the angle of depression to the top of the tower, the vertical distance from the top of the building to the top of the tower is (78−h) m.
tan(30°)=d78−h
31=7878−h
78−h=378
78−h=1.73278
78−h=45.03
h=78−45.03
h=33 m
Therefore, the height of the tower is approximately 33 m.