D, the second derivative of h with respect to time is going to be equal to, well, the derivative of this first term with respect to time, it's going to be the derivative of this with respect to h times the derivative of h with respect to time. So this is equal to negative 1 4th, that's the derivative of this term with respect to h, and then we want to multiply that times the derivative of h with respect to time. This comes just straight out of the chain rule. And then the derivative of a constant, how does that change with respect to time? It's not gonna change, that is just going to be zero. So just like that, we were able to find the second derivative of h with respect to time. And now, what does this tell us?