We actually now know two points that lie on that line, so we can literally find the slope of that line and then the y-intercept, the b there. Or we could just say it's a solution to this system of equations, and they're actually mathematically equivalent. So let's solve for m first. And if we want to solve for m, we want to cancel out the b. So let me rewrite this top equation just the way it's written over here. So we have m times the mean of the x squareds plus b times the mean of... Actually, we could even do it better than that. One step better than that is to actually, based on the work we did in the last video, we can just subtract this bottom equation from this top equation.