12. (6 points) A ship, on its first trip, travels 420 kilometers downstream and 80 kilometers upstream, taking 11 hours; on its second trip, it uses the same amount of time to travel 240 kilometers downstream and 140 kilometers upstream. How many hours does it take for this ship to travel 198 kilometers downstream? $\qquad$
【Solution】Solution: The speed of sailing downstream is the speed of sailing upstream:
$$
\begin{aligned}
& (420-240) \div(140-80), \\
= & 180 \div 60, \\
= & 3 \text { (times); }
\end{aligned}
$$

The speed of sailing downstream per hour is:
$$
\begin{aligned}
& (420+80 \times 3) \div 11, \\
= & 660 \div 11, \\
= & 60 \text { (km); }
\end{aligned}
$$

This ship needs to sail 198 km downstream:
$$
198 \div 60=3.3 \text { (hours); }
$$

Answer: This ship needs 3.3 hours to sail 198 km downstream.
The answer is: 3.3.