Final answer:
The average rate of change of the trend line y = 0.390x + 20.2 is 0.390.
Step-by-step explanation:
The average rate of change of a linear function is equal to its slope. In the equation y = 0.390x + 20.2, the coefficient of x, which is 0.390, represents the slope. Therefore, the average rate of change of this trend line is 0.390.