So here we're told the function K of t gives the amount of ketchup in kilograms produced in a sauce factory by time in hours on a given day. So this is really quantity as a function of time. It isn't rate. 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.