So your width is going to be delta x of each of those rectangles. And then your height is going to be the value of the function evaluated someplace in that delta x. If we're doing a right Riemann sum, we would do the right end of that rectangle or of that subinterval. And so we would start at our lower bound, a, and we would add as many delta x's as our index specifies. So if i is equal to one, we add one delta x. So we'd be at the right of the first rectangle. If i is equal to two, we add two delta x's.