So let's say that this right over here is the line y equals 1. So this is what we're going to rotate it around, y equals 1. So the first thing we want to do is visualize what we're doing. And we actually care about the interval. So let's say that the interval is between this point right over here, where the two points intersect. And let's say between that and x is equal to 4. So let's say that this right over here, so this is x equals 4.