The average rate of change would be the gradient of the straight line that connects the coordinates (1, 1) and (3, 9)
The slope = Vertical distance ÷ Horizontal Distance
The slope = (9-1) ÷ (3-1)
The slope = 8 ÷ 2
The slope = 4
This means, for every increase of one unit of 'n' there's an increase of 4 units on y-axis
