There are four layers of glass plates, placed on top of each other such that bottom one has thickness $$a_1$$ and refractive index $$n_1 = 2.7$$. Next one has thickness $$a_2$$ and refractive index $$n_2 = 2.43$$. The third one and the top one have thickness $$a_3$$ and $$a_4$$ and refractive indices $$n_3$$ and $$n_4$$ respectively. Three rays starting at the same moment from $$A_1$$, $$A_2$$ and $$A_3$$ reach points $$B_2$$, $$B_3$$, $$B_4$$ at the same time, with their angles of incidence being critical angle. You are given $$A_1B_1 = A_2B_2 = A_3B_3 = A_4B_4 = b = 10$$ mm. Choose correct statement (s). [In four significant figures]