(a) The diver would hear the sound first.
(b) The sound is heard by the diver first because sound travels faster in water than in air.
(c) As we know, the speed of sound in water (1450 ms-1 ) is more than the speed of sound in air (330 ms-1) so if ‘t’ is the time taken by sound to reach the boat man, then the time taken by sound to reach the diver is 0.25t as sound travels nearly four times faster in water.