12. (3 points) A ship sails from Port A to Port B, traveling 24 kilometers per hour against the current. After reaching Port B, it returns to Port A with the current. It is known that the downstream journey takes 5 hours less than the upstream journey, and the speed of the current is 3 kilometers per hour. The distance between Port A and Port B is $\qquad$ meters.
12. (3 points) A ship sails from Port A to Port B, traveling 24 kilometers per hour against the current. After reaching Port B, it returns to Port A with the current. It is known that the downstream journey takes 5 hours less than the upstream journey, and the speed of the current is 3 kilometers per hour. The distance between Port A and Port B is __ $\frac{200}{3}$ kilometers.
【Solution】Solution: The downstream speed is:
$$
24+3+3=30 \text { (km/h); }
$$

The distance between Port A and Port B is:
$$
\begin{array}{l}
5 \div\left(\frac{1}{24}+\frac{1}{30}\right) \\
=5 \div \frac{3}{40}, \\
=\frac{200}{3} \text { (km); }
\end{array}
$$

Answer: The distance between Port A and Port B is $\frac{200}{3}$ kilometers.
Therefore, the answer is: $\frac{200}{3}$.