But these are the rates of entering and the rates of exiting. So how much water, they're asking how many cubic feet of water flow into, so enter into the pipe during the 8 hour time interval. So if you have your rate, this is the rate at which things are flowing into it, they give it in cubic feet per hour. If you multiply it times some change in time, even infinitesimally small change in time, so d t, this is the amount that flows in over that very small change in time. And so what we want to do is we want to sum up these very small, these amounts over very small changes in time to go from time is equal to 0 all the way to time is equal to 8. So this expression right over here, this is going to give us how many cubic feet of water flow into the pipe. Once again, what am I doing?