#### Problem 23E

23. At noon, ship $\mathrm{A}$ is $100 \mathrm{~km}$ west of ship $\mathrm{B}$. Ship $\mathrm{A}$ is sailing south at $35 \mathrm{~km} / \mathrm{h}$ and ship $\mathrm{B}$ is sailing north at $25 \mathrm{~km} / \mathrm{h}$. How fast is the distance between the ships changing at 4:00 PM?