after the second stone is released
separation of the stones at this instant of dropping of the second stone =
1/2*10*2*2=20 m
discussing motion from the frame of the second stone .
rel. velocity of 1 stone = v12= 9.8*2+2.2*2 = 20 m/s
sepration of the stones after 1.5 s= 20*1.5+20= 50m