A tank holds a layer of oil, 1.58 m thick, which floats on a layer of syrup that is 0.66 m thick. Both liquids are clear and do not intermix. A ray, which originates at the bottom of the tank on a vertical axis, crosses the oil-syrup interface at a point 0.90 m from the axis. The ray continues and arrives at the oil-air interface, 2.00 m from the axis and at the critical angle. The index of refraction of the syrup is closest to: