Given:Refractive index of the flint glass, μf​ = 1.620Refractive index of the crown glass, μc​ = 1.518Refractive angle of the flint prism, Af​ = 6°Now,Let the refractive angle of the crown prism be Ac​ .For the net deviation of the mean ray to be zero,Deviation by the flint prism = Deviation by the crown prismi.e., (μf​ − 1)Af​  = (μc​ − 1)Ae​ ⇒ Ac​ =(μe​−1μf​−1​)Af​⇒ Ac​ =(1.518−11.620−1​)×6.0∘=7.2∘Thus, the refracting angle of the crown prism is 7.2°.