Answer
a. 0.994 s
b. 4.52 s
Work Step by Step
a. For the fish, use the speed of sound in seawater to find the time.
$$t=\frac{1550m}{1560m/s}=0.994s$$
b. For the people onboard the boat, use the speed of sound in air to find the time.
$$t=\frac{1550m}{343m/s}=4.52s$$