Light traveling in a material of refractive index n, is incident at angle , with respect to

Light traveling in a material of refractive index n, is incident at angle θ, with respect to the normal at the interface with a slab of material that has parallel faces and refractive index n2. After the light passes through this material, it is refracted into a material with refractive index n, and in this third material it makes an angle of θ3 with the normal.
(a) Find θ3 in terms of θ, and the refractive indexes of the materials.
(b) The ray in the third material is now reversed, so that it is incident on the n3-to-no interface with the angle θ3 found in part (a). Show that when the light refracts into the material with refractive index n" the angle it makes with the normal is angle θ. This shows that the refracted ray is reversible. (c) Are reflected rays also reversible? Explain.