What does the definite integral from zero to four of K prime of t dt represent? Once again, pause the video and see if you can work through it. Well, K of t is the amount of ketchup as a function of time. 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.