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 $$\theta = 30^\circ$$. The interfaces of the glass layers are parallel to each other. The refractive indices of different glass layers are monotonically decreasing as $$n_m = n - m \triangle n$$, where $$n_m$$ is the refractive index of the $$m^{th}$$ slab and $$\triangle n = 0.1$$ (see the figure) The ray is refracted out parallel to the interface between the $$(m - 1)^{th}$$ and $$m^{th}$$ slabs from the right side of the stack. What is the value of m?