And they wanna know the rate of change two days after studying. Well, the rate of change, I can take the derivative of this with respect to time. So let's do that. So let's take the derivative, the derivative of the number of words I know with respect to time is going to be equal to, well, we have this 80 out front. That's just a constant. And now I can apply the chain rule right over here. So the derivative of one minus 0.1t whole thing squared with respect to one minus 0.1t is going to be, so I'm essentially taking the derivative of this whole pink thing, with this whole expression squared with respect to the expression.