To find the height from which the stone fell, we can use the equation of motion:
s = ut + (1/2)at^2
Where: s = distance traveled by the stone (2.2m) u = initial velocity of the stone (0 m/s, as the stone is falling) a = acceleration due to gravity (-9.8 m/s^2) t = time taken for the stone to travel past the window (0.28s)