Two optical media have a plane boundary between them. Suppose 1er is the critical angle of incidence

Question:

Two optical media have a plane boundary between them. Suppose θ1er is the critical angle of incidence of a beam and θ1 is the angle of incidence at which the refracted beam is perpendicular to the reflected one (the beam is assumed to come from an optically denser medium). Find the relative refractive index of these media if sin θ1er /sin θ1 = η = 1.28.