The average rate of change is an algebra thing, whereas the instantaneous rate of change is a calculus thing. Since this is not a straight line we are simply finding the slope of the straight line that connects the 2 coordinates (4, y) and (9, y). To find the y's in each case, sub in the x value and solve for y:
If when x = 4, then and the coordinate is .
Likewise for the other coordinate when x = 9. and the coordinate is