Answer:
Rate of change = 6 miles per hour
Step-by-step explanation:
Rate of change of the line is represented by the slope of the line.
Formula to get the rate of change is,
m = 
From the graph attached,
Given straight line is passing through two points (2, 12) and (4, 24).
Rate of change = 
= 
= 6
Rate of change of the line = 6 miles per hour
Therefore, rate of change of the graph will define the speed of Arlene.