A bird in air is dividing vertically over a tank with speed `6 cm//s`. The base of the tank is silvered. The fish in the tank is rising upward along the same line with speed `4 cm//s`. (Take: `mu_("water") = 4//3)`. Find:
(a) The speed of the image of the fish asseen directly by the bird.
(b) The speed of the image of the bird relative to the fish looking upwards.