3. (12) (a) Sonar is used for commercial fishing to detect schools of fish which have internal air sacks. Assume that the sonar is generated with a power of 0.18 W at 50 kHz that spreads in a 35o cone as it propagates into water. If 18% of the sound energy reaching the school of fish is reflected and scattered uniformly, calculate the power density reaching the school of fish, and the power density reflected from the fish at 55 meters. (Attenuation in water at 50 kHz is 13 dB/km.) (3) (b) What would happen to the power density of the sonar reflected from the fish at 55 m, if the frequency of the sound waves were increased by 10%