Well, this right here is the mean of their product from your sample, minus the mean of your sample Ys times the mean of your sample Xs. And this should start looking familiar. This should look a little bit familiar, because what is this? This was the numerator. This right here is the numerator when we were trying to figure out the slope of the regression line. So we tried to figure out the slope of the regression line. Let me just rewrite the formula here just to remind you.