Freeway noise lessens as the distance from the freeway increases. Some readings are shown in the table below.
Distance (yards)
| Noise (decibels) |
| 60 |
140 |
| 70 |
110 |
| 90 |
10 |
What is the average rate of change in the noise level as you go from 70 to 90 yards away from the freeway?