A sound pulse is generated at the underside of a boat. It moves through the water and is reflected by a shoal of fish. After $1.2\,\text{ s}$, the sound returns to the boat. The speed of sound in the water is $1500\,\text{ m s}^{-1}$. Determine the depth of the shoal of fish below the bottom of the boat.
- A$450\,\text{m}$
- B$900\,\text{m}$
- C$1800\,\text{m}$
- D$3600\,\text{m}$