A cubical container is filled with liquid of refractive index 1.2. A convex lens having radius of curvature $R_1=20$ cm and $R_2=24$  cm is fixed in one face of cuboid. Parts of concave lens having (concave lens is cut into two equal parts along its principal axis) having focal length 20 cm in liquid are placed as shown (refractive index of material of concave lens 1.15). An interference pattern is obtained on screen AB for source S. Distance between images formed by parts of concave lens is X mm and fringe width of pattern formed on the screen is Y mm. (Consider rays passing through parts of the concave lens only,  $\lambda$ for source is 500 nm in liquid and refractive index of material of convex lens is 1.5)