Given, Focal length of objective, fo = 150 cm
Focal length of eye-piece, fe = 5 cm
Height of tower, H = 100 m
Distance of tower, u = 3 km
Magnification of telescope is given by:
m = -fo/fe (1 + fe/D)
m = -150/5 (1 + 5/25) = -30
Also, m = tanβ/tanα
tanα = H/u = 100/3000 = 1/30
tanβ = m tanα
tanβ = -30 x (1/30) = -1
Height of the image of the tower, H' = -m x (u/D) = -30 x 25/3000 = -1/4 cm = -0.25cm