15. (15 points) There is a road between places $A$ and $B$. Two cars, Car A and Car B, start from $A$ and $B$ respectively at the same time. Car A's speed is 50 kilometers/hour. After 1 hour, the two cars meet for the first time. Then the two cars continue to drive, each reaching $B$ and $A$ respectively, and immediately return. The distance between the second meeting point and the first meeting point is 20 kilometers. Find:
(1) The distance between $A$ and $B$.
(2) The speed of Car B.
【Solution】Solution: (1) When the second meeting point is 50+20=70 kilometers away from location $A$, the distance between $A$ and $B$ is:
$$
\begin{aligned}
& (50 \times 3+50+20) \div 2 \\
= & 220 \div 2, \\
= & 110 \text { (km). }
\end{aligned}
$$

Answer: The distance between $A$ and $B$ is 110 kilometers.
The speed of car B is:
$$
\begin{array}{l}
110 \div 1-50 \\
=110-50, \\
=60 \text { (km/h). }
\end{array}
$$

Answer: The speed of car B is 60 km/h.
When the second meeting point is 50-20=30 kilometers away from location $A$:
$$
\begin{array}{l}
(50 \times 3+50-20) \div 2 \\
=180 \div 2, \\
=90 \text { (km). }
\end{array}
$$

Answer: The distance between $A$ and $B$ is 90 kilometers.
The speed of car B is:
$$
\begin{array}{l}
90 \div 1-50 \\
=90-50, \\
=40 \text { (km/h). }
\end{array}
$$

Answer: The speed of car B is 40 km/h.