Two sightings are taken 4000 ft disatnce from the base of the tower.

Angle of elevation to the top of the sky pod is .

Angle of elevation to the top of the tower is .

Draw the diagram for situation:

Here represents the height of the tower above the sky pod. 

  represents the height of the tower upto the sky pod.

From the figure,

ft.

Consdier

.

Substitute in the above expression.  

ft.

Thus, the height of the tower above the sky pod is ft.

Height of the tower above the sky pod is ft.