Time taken by the sonar pulse to return, t = 1.02 s
Speed of sound in saltwater, v = 1531 ms-1
We have to determine how far away is the cliff the submarine
Distance of the cliff from the submarine = Speed of sound * Time taken
Distance of the cliff from the submarine = 1.02 x 1531 = 1561.32 m
Distance traveled by the sonar pulse during its transmission and reception in water = 2 x Actual distance = 2d
Actual Distance, d= (Distance of the cliff from the submarine)/2
= 1561/2
= 780.31 m