1400 minus 1300 is 1100. And then 1100 divided by 625 is a small number, it's one point something, but it is a positive number. And that's the important thing here. So this thing, all of this business, it is positive. So the second derivative is positive, which means the slope is increasing, at least right at our starting point our slope is increasing, which tells us that since our slope is increasing from that point, and frankly the fact that it's increasing at all, and that we know that W is an increasing function, tells us that our estimate in part A is an underestimate. So this is the case that we're dealing with. So our estimate in part A is an underestimate of the actual amount of solid waste in the landfill at time t equals 1 fourth.