In a Young's double slit experiment, d=1 mm , λ=6000A˚ and D=1 m . The slits produce same intensity on the screen. The minimum distance between two points on the screen having 75% intensity of the maximum intensity is:
(a) 0.45 mm
(b) 0.40 mm
(c) 0.30 mm
(d) 0.20 mm