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. Slope is equal to rise over run. You might have seen that when you first learned algebra. Or another way of writing it, it's change in y over change in x.