Solution:
Let us consider, town A at point $(0,0)$. Therefore, town B will be at point $(36,15)$.
Distance between points $(0,0)$ and $(36,15)$
$d=\sqrt{(36-0)^{2}+(15-0)^{2}}=\sqrt{(36)^{2}+(15)^{2}}=\sqrt{1296+225}=\sqrt{1521}=39$
In section $7.2, \mathrm{~A}$ is $(4,0)$ and $\mathrm{B}$ is $(6,0)$
$A B^{2}=(6-4)^{2}-(0-0)^{2}=4$
The distance between town $A$ and $B$ will be $39 \mathrm{~km}$. The distance between the two towns $A$ and $B$ discussed in Section $7.2$ is $4 \mathrm{~km}$.