The sequence an = 1(3)n − 1 is graphed below: coordinate plane showing the points 1, 1; 2, 3; and 3, 9 find the average rate of change between n = 1 and n = 3.

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

Use a calculator basically