To solve this problem it is necessary to apply the concepts related to the kinematic equations of motion.
By definition we know that speed can be expressed as
[tex]v= \frac{d}{t}[/tex]
Where,
t = time
d = distance
For this specific case we know that the speed traveled corresponds to the round trip, therefore
[tex]v = \frac{2d}{t}[/tex]
Re-arrange to find t (The time taken to here the echo)
[tex]t = \frac{2d}{v}[/tex]
Replacing with our values we have that the distance is equal to 65m
[tex]t = \frac{2*65}{1530}[/tex]
[tex]t = 0.085s[/tex]
Therefore the time before the dolphin hears the echoes of the clicks is 0.085s
