(Distance between aircraft) An aircraft is $144 \mathrm{km}$ east of an airport and is travelling west at $200 \mathrm{km} / \mathrm{h}$. At the same time, a second aircraft at the same altitude is $60 \mathrm{km}$ north of the airport and travelling north at $150 \mathrm{km} / \mathrm{h}$. How fast is the distance between the two aircraft changing?