Answer: (b) 1450m/s
Explanation:The time it takes a sound wave to travel to a particular surface is equal to the time it takes to reflect back to its source.
As such, it would take twice as much time to get to the depth travelled for the sound wave to reflect back to the ship(source).
Therefore, since it takes 5seconds for the reflection to get back to the ship.
Then it takes {5/2}seconds ...which is an equivalent of 2.5seconds for the sound to get to the 3625m depth.
Therefore, the speed(velocity) of the sound waves which is a measure of how fast the sound moves is;
Speed(v)= (3625m)/(2.5s)
The speed of the sound wave is therefore equal to 1450m/s.