So K prime of t, that's going to be the rate at which our amount of ketchup is changing as a function of time. But once again, when you're taking the area under the rate curve, that tells you the net change in the original quantity, in the amount of ketchup. And it's the net change between time zero and time four. So let's see which of these choices match up to that. The average rate of change of the ketchup production over the first four hours, no, that does not tell us the average rate of change. There's other ways to calculate that. The time it takes to produce four kilograms of ketchup.