The answer would be increased number <span />of rod cells.Hope this helps :)
In sound waves, the particles move in the same direction as the wave is moving, so you wouldn't be able to see them like ripples in the air, instead they make areas in the air where the particles are more squished together, and areas where the particles are further apart.
The change needed is from 8 to 28, a change of 20 m/s. At a rate of 2m/s/s it will take 10 seconds for it to happen (2x10=20). I hope this helps.
