So we don't know yet what W actually does look like, but they tell us it's an increasing function. So at time zero, it has 1,400 tons in it, they tell us that right up here, and then it increases. We don't know what the function actually does look like, but let's say that that is W. So what they're saying in problem A, is they're saying use a tangent line to the graph at T equals zero. So there's, let me actually, let me draw W a little bit differently. So W might look like this, W might look like this. So what they're saying is find the tangent line, find the slope of that tangent line at T equals zero. So there's some slope right over there.