Now the next thing that we need to do in order to actually calculate this area is think about what is the width. So let's call the width of any of these rectangles. And for these purposes, or the purpose of this example, I'm going to assume that it's constant. Although you can do these sums where you actually vary the width of the rectangle, but then it gets a little bit fancier. So I want an equal width. So I want delta x to be equal width. And to think about what that has to be, we just have to think, what's the total width that we're covering?