A monochromatic light is travelling in a medium of refractive index n = 1.6. It enters a stack of glass layers from the bottom side at an angle = 30°. The interfaces of the glass layers are parallel to each other. The refractive indices of different glass layers are monotonically decreasing as n m = n - m n, where n m is the refractive index of the m th slab and An = 0.1 (see the figure). The ray is refracted out parallel to the interface between the (m -l) th and m th slabs from the right side of the stack. What is the value of m?