The Bird & Fish Problem

A bird moving vertically downwards observes a fish moving vertically upwards with a velocity $12 \text{ m/s}$ . The fish observes the bird moving down with $16 \text{ m/s}$ .

Take the refractive index of water as 4/3. The bird emits a sound of frequency $320 \text{ Hz}$ . Find the frequency of sound heard by the fish.

Assume the velocity of sound in air as $329\text{ m/s}$ and the velocity of sound in water as $1316\text{ m/s}$ .