We know what v prime of x is. If we wanted to do v prime of u of x, we would just replace wherever we see an x with the u of x. So this is going to be equal to v prime of u of x. And you just use it, you're taking the derivative of the green function with respect to the blue function. So it's going to be one over the natural log of four, natural log of four, times, instead of putting an x there, it would be times u of x. Times u of x. And of course, that whole thing times u prime of x.