With initial condition, at time zero, w is equal to 1400. And the units in this problem, it was 1400 tons, they told us, 1400 tons. So, it might seem strange to see a differential equations problem on an AP exam. You say, well, you know, this isn't fair. This isn't a differential equations class. And the thing to keep in mind is, if on an AP exam you see differential equations, they're really asking you to solve a differential equations that can be solved using the skills that you would learn in an AP class. And the main differential or class of differential equations that you could solve are the ones, are separable differential equations.