At a point on the screen at a distance D from the slits in standard YDSE experiment, 3rd maxima is observed at t=0 . Now screen is slowly moved with constant speed away from the slits in such a way That the centre of slits and centre of screen always lie on the same line and at t= 1 sec the intensity at that point is observed to be 3/4th of maximum intensity in between 2nd and 3rd maxima. The speed of screen is
