Answer:1.902 m
Step-by-step explanation:
Given
height of apartment=1.5 m
It takes 0.21 sec to reach the bottom from apartment
So



i.e. if ball is dropped from top its velocity at window is 6.11 m/s
So height of upper floor above window

where s= height of upper floor above window
here u=0


s=1.902 m