ANSWER
15 miles per hour
Step-by-step explanation
To find the rate of change of the function, we simply have to find the slope of the graph function.
To do this, we will use the two points given on the graph:
(1, 15) and (3, 45)
We will use the formula:
where (x1, y1) = (1, 15)
(x2, y2) = (3, 45)
Therefore:
The rate of change of the function is 15 miles per hour.