We've done that multiple times, so times dx. This is the thing that we want to sum up. This is the thing that we want to sum up over our interval. Our interval, let's see, this point right over here where the square root of x is equal to 1, that's just going to be x equals 1. This is just x equals 1 over here. We said that we would do this all the way until x equals 4. This was kind of our end of our interval.