13. (3 points) A large river, in the middle of the river (main channel) the water flows at a speed of 10 kilometers per hour, and along the bank the water flows at a speed of 8 kilometers per hour. A boat travels downstream in the middle of the river, and in 10 hours it covers 360 kilometers. This boat needs to return to the original place along the bank, it will take $\qquad$ hours.
【Solution】Solution: The still water speed of the boat is:
$$
\begin{array}{l}
360 \div 10-10, \\
=36-10, \\
=26 \text { (km/h); }
\end{array}
$$

To return to the original place, it needs:
$$
\begin{array}{l}
360 \div(26-8), \\
=360 \div 18, \\
=20 \text { (hours); }
\end{array}
$$

Answer: This boat needs 20 hours to return to the original place along the shore. Therefore, the answer is: 20.