Geometrical Optics

A fish rising vertically upward with a uniform velocity of \(8 \mathrm{~ms}^{-1}\), observes that a bird is diving vertically downward towards the fish with the velocity of \(12 \mathrm{~ms}^{-1}\). If the refractive index of water is \(\frac{4}{3}\), then the actual velocity of the diving bird to pick the fish, will be __________ \(\mathrm{ms}^{-1}\).