Given here, Angle of depression=30 degrees.
Height of tower = 100 m
It will make a triangle if you take an point to represent car.
Rotate your figure to left side.
30 degrees will shift to down & 100m will be base.
let the distance between building and car be x m.
tan 30 degrees=x m/100m
Simply it, you will get 57.74 m as the answer.