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