A pulse of sound is generated at the underside of a boat. The sound moves through the water and is reflected by a shoal of fish. The reflected sound returns to the boat $1.2\,\text{s}$ after it is produced. The speed of sound in the water is $1500\,\text{m s}^{-1}$. How far beneath the bottom of the boat is the shoal of fish?
- A$450\,\text{m}$
- B$900\,\text{m}$
- C$1800\,\text{m}$
- D$3600\,\text{m}$