The average rate of change is the same as the slope. Even though this graph is a parabola, we still use the slope formula with the corresponding points. Had the question asked for the instantaneous rate of change, we would have needed to find a derivative.
Slope formula: (y2 - y1) / (x2 - x1)
Point 1: (0,4)
Point 2: (2,8)
(8 - 4) / (2 - 0)
4 / 2
2
The average rate of change from x = 0 to x = 2 is 2.
Hope this helps!