4- 204 A car transports daily necessities from Town A to Village B, traveling 20 kilometers uphill, 14 kilometers downhill, and 5 kilometers on flat road. It then transports grain from Village B back to Town A. The time difference for the round trip is 10 minutes. It is known that the speed ratio of the car when going uphill, downhill, and on flat road is 3 : 6 : 5. Try to find:
(1) The average speeds of the car when going uphill, downhill, and on flat road,
(2) The time required for the car to travel from Town A to Village B, and from Village B to Town A.
［Solution］ (1) According to the problem, let the average speeds of the car when going uphill, downhill, and on a flat road be $3 v, 6 v, 5 v$ (km/h) respectively.
Since $\left(\frac{20}{3 v}+\frac{14}{6 v}+\frac{5}{5 v}\right)-\left(\frac{20}{6 v}+\frac{14}{3 v}+\frac{5}{5 v}\right)=\frac{1}{6}$,
which simplifies to $\frac{6}{3 v}-\frac{6}{6 v}=\frac{1}{6}$, thus $v=6$.
Therefore, the average speeds when going uphill, downhill, and on a flat road are $18, 36, 30$ (km/h) respectively.
(2) The time required for the trip from Town A to Village B is:
$$
\begin{aligned}
& \frac{20}{18}+\frac{14}{36}+\frac{5}{30}=\frac{1}{18}(20+7+3) \\
= & \frac{30}{18}=1 \frac{2}{3} \text { (hours). }
\end{aligned}
$$

The time required for the trip from Village B to Town A is
$$
1 \frac{2}{3}-\frac{1}{6}=1 \frac{1}{2} \text { (hours). }
$$