This is the rate of change of the rate at time seven minus the rate of change of the rate at time two. So I would rule that one out as well. Let's do one more of these. So here we have, here we have the depth of water in a tank is changing at a rate of, r of t is equal to 0.3 t, centimeters per minute, where t is the time in minutes. At time t equals zero, the depth of the water is 35 centimeters. What is the change in the water's depth during the fourth minute? So let's pause the video again and see if you can figure this out again and figure out what expression can we use to solve the problem.