Can someone please help me out with this question:

Using the graph, find the instantaneous rate of change at:

a) x = -2

b) x = -1

c) x = 3

I only need to know how to do one of them, so I can use the same formula/technique for b & c. The problem is that I can't post the graph on here so I just need the technique on how to find it.

I have to put this as geometer sketchpad because that's where the file comes from. I'm given a graph and 2 points which I can move... I'm not sure how to find instananeous rate though... Can anyone help me out?

Thanks