2. A ship travels 80 km downstream and 48 km upstream in a total of 9 hours; it travels 64 km downstream and 96 km upstream in a total of 12 hours. Find the speed of the ship in still water.
【Answer】 $2 \mathrm{~km} / \mathrm{h}$
【Solution】Method one: Let the boat speed be $x \mathrm{~km} / \mathrm{h}$, and the water speed be $\mathrm{y} \mathrm{km} / \mathrm{h}$
$$
\left\{\begin{array}{l}
\frac{80}{x+y}+\frac{48}{x-y}=9 \\
\frac{64}{x+y}+\frac{96}{x-y}=12
\end{array}\right.
$$

Substitution method, $a=x+y ; b=x-y$
Solving yields $x=12, y=2$, so the water speed is 2 kilometers/hour
Method two:
Traveling 80 kilometers downstream and 48 kilometers upstream takes 9 hours, traveling 64 kilometers downstream and 96 kilometers upstream takes 12 hours, scaling up we get:

Traveling 320 kilometers downstream and 192 kilometers upstream takes 36 hours, traveling 192 kilometers downstream and 288 kilometers upstream takes 36 hours, comparing, traveling 128 kilometers downstream takes the same time as traveling 96 kilometers upstream. That is, traveling 4 kilometers downstream takes the same time as traveling 3 kilometers upstream,

Traveling 80 kilometers downstream and 48 kilometers upstream can be equivalently replaced by traveling 144 kilometers downstream, or 108 kilometers upstream

Downstream speed $=144 \div 9=16 \mathrm{~km} / \mathrm{h}$, upstream speed $=108 \div 9=12 \mathrm{~km} / \mathrm{h}$
Still water speed: $（ 16+12 ） \div 2=14 \mathrm{~km} / \mathrm{h}$