Light travels from water (n1=1.33) into a layer of oil whose index of refraction at one instant is n2=1.04 and increasing at 0.0020 s−1. The angle of incidence in the water is a constant 30∘, and at that instant the angle of refraction in the oil is 40∘. Find the instantaneous rate of change of the angle of refraction, dθ2/dt, in rad/s at that instant.