a) Compression is a part of a longitudinal wave in which the particles of the medium are close to each other which reduces the volume of the medium.
Rarefaction is also a part of a longitudinal wave in which the particles of the medium are farther apart from each other which increases the volume of the medium.
b) Speed = 330 m/s
Distance = 1.32 km = 1320 m
Time = distance/speed = 1320/330 = 4s