Answer:
The sniper shoot from 870.775 feet vertical distance.
Explanation:
Refer the attached figure
Height of victim = AB = 4.5 ft.
Distance between tower and victim BC = 780 feet
The angle of elevation =

Let DE be x
AB = CE = 4.5 feet
BC =AE = 780 feet
Height of tower = DE+CE=x+4.5
In ΔDAE

Height of tower = DE+CE=x+4.5=866.275+4.5=870.775 feet
Hence the sniper shoot from 870.775 feet vertical distance.