So let's just figure out what our second derivative is at time 0. It's going to be equal to 1 over 625 times W of 0, which we know, minus 300. Well, W of 0, the amount of waste we have at time 0, they told us in the problem, is 1400 tons. 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.