Two sources of sound placed close to each other are emitting progressive waves given by y, = 4 sin 600 t and y = 5 sin 608 t. An observer located near these two sources of sound will hear : (a) 4 beats per second with intensity ratio 25: 16 between waxing and waning. (b) 8 beats per second with intensity ratio 25: 16 between waxing and waning (c) 8 beats per second with intensity ratio 81 1 between waxing and waning (d) 4 beats per second with intensity ratio 81 : 1 between waxing and waning