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. The problem being, what is the change in the water's depth during the fourth minute? Alright, so we've just talked about if you're trying to find the change in a value, you could take the integral of the rate function over the appropriate time. So we're talking about during the fourth minute.