5. There are cable cars running back and forth between two ski resorts, A and B. All 80 cable cars travel on a circular track in the same direction, with the same distance between adjacent cable cars. Ming, sitting in a cable car, encounters an oncoming cable car every 15 seconds. The travel time from A to B is $\qquad$ minutes.
\begin{tabular}{c}
5 \\
\hline 20
\end{tabular}