And so we can say the second derivative of W as a function of T is equal to 1 over 625 times W as a function of T, which is a function of T, minus 300. So we've done the first part. We've found out the second derivative of W in terms of just W. Now let's try to address the second part of their question. So we did the first part. Now use what we just figured out to determine whether your answer in part A is an underestimate or an overestimate of the amount of solid waste that the landfill contains at time 1 fourth. So in part A, we found the slope of the tangent line at time equals 0. And we use that slope to extrapolate out to 3 months, or time equals 1 fourth, 1 fourth of a year.