You basically have to find the slope, to find the average rate of change, because finding the slope and finding the average rate of change is basically the same thing.
Here's the formula :
So here, all you'd have to do is simply pick two points, and insert them into this formula. Say you take the points (-2, -2) and (0,-3). You would start from the y-intercept of the second point, and insert them all into the formula.
which would turn into 
. And so since you want a good, stable number, and not just a fraction, you would divide -1 and 2, and the average rate of change would be -0.50.
AVERAGE RATE OF CHANGE : -0.50
Here's the formula :
So here, all you'd have to do is simply pick two points, and insert them into this formula. Say you take the points (-2, -2) and (0,-3). You would start from the y-intercept of the second point, and insert them all into the formula.
AVERAGE RATE OF CHANGE : -0.50