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Civil engineers often design earth berms (mounds of dirt covered with grass) on the sides of major highways in order to absorb and reflect sound from vehicles. This reduces the noise levels for properties near the highway. The following table gives values of the sound level (measured in decibels) at varying distances away from the edge of a highway (measured in meters).

Distance (meters from edge of highway) 0 20 45 50 65
Sound level (decibels) 81 64 59 57 52

Identify the interval between two consecutive distance measurements which experiences the magnitude of the greatest rate of decrease in sound level, as measured in decibels per meter.

Then, using the rate of decrease between 50 meters and 65 meters, and assuming the rate of decrease continues identically, predict the distance from the highway at which the sound level would drop to 45 decibels.

Interval of Greatest Rate of Decrease

Prediction for Distance to reach 45 decibels

0 meters to 20 meters

20 meters to 45 meters

45 meters to 50 meters

50 meters to 65 meters

21 meters

70 meters

86 meters

135 meters

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