How to do question no 6 of maths ncert ex 9.1

Let the boy was standing at point S initially. He walked towards the building and reached at point T.
So, it can be observed that PR = PQ – RQ = (30 – 1.5) = 28.5 m = 57/2 m
Now, in triangle PAR, PR/AR = tan 30
57/2AR = 1/√3
So, AR = (57 √3 / 2)m
In triangle PRB, PR/BR = tan 60
57/2BR = √3
So, BR = (57/2√3 ) = (19√3 /2) m
Now, ST = AB = AR – BR = (57 √3 / 2) – (19√3 /2) = 19√3 m