So that's three, this is three, and this is three. And so the question is, how do we define the height of these subdivisions which are going to end up being rectangles? And that's where the right Riemann sum applies. If we were doing a left Riemann sum, we would use the left boundary of each of the subdivisions and the value of the function there to define the height of the rectangle. So this would be doing a left Riemann sum. But we're doing a right Riemann sum. So we use the right boundary of each of these subdivisions to define the height.