Actually, let me make it clear that this coordinate right here is the point a, f of a. So how do we find the slope between these two points? Or more generally, of this entire line? Because a line has the slope is consistent the whole way through it. And we know that once we find the slope, that's actually going to be the value of this f. That's all a review of your algebra. But how do we do it? Well, a couple of ways to think about it.