So the derivative with respect to time. I'm not taking the derivative with respect to r. I'm taking the derivative with respect to time. So on the left hand side right over here, I'm going to have the derivative of our area. Actually, let me just write it in that green color. I'm going to have the derivative of our area with respect to time on the left hand side, And on the right-hand side, what do I have? Well, if I'm taking the derivative of a constant times something, I can take the constant out. So let me just do that.