\[V_{1} - скорость\ поезда;\]
\[V_{2} - скорость\ автобуса.\]
\[1 - весь\ путь.\]
\[(2) - (1):\ \ \ \ \frac{5}{5V_{1}} = 5\]
\[\text{\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }\frac{1}{V_{1}} = 5\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 5V_{1} = 1\]
\[\text{\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }V_{1} = \frac{1}{5}\]
\[t = 1 \cdot V_{1};\ \ \ \ \ \ t = 1\ :\frac{1}{5} = 5\ ч.\]
\[Ответ:5\ ч.\]