When the rectangular metal tank in the figure below is filled to the top with an unknown liquid, observer O, with eyes level with the top of the tank, can just see the corner E. A ray that refracts toward O at the top surface of the liquid is shown. If D = 81.0 cm and L = 1.15 m, what is the index of refraction of the liquid?

When the rectangular metal tank in the figure below is filled to the top with an unknown liquid, observer O, with eyes level with the top of the tank, can just see the corner E. A ray that refracts toward O at the top surface of the liquid is shown. If D = 81.0 cm and L = 1.15 m, what is the index of refraction of the liquid?