12. (10 points) At 8:00 AM, Xiao Cheng and Xiao Chen set off from locations A and B, respectively, heading towards each other. They met at 9:40 AM.
Xiao Cheng said: “If I had traveled 10 kilometers more per hour, we would have met 10 minutes earlier.”
Xiao Chen said: “If I had set off half an hour earlier, we would have met 20 minutes earlier.”
If both of them are correct, then the distance between A and B is $\qquad$ kilometers.
【Solution】Solution: 9: $40-8: 00=1$ hour 40 minutes $=\frac{5}{3}$ hours 1 hour 40 minutes -10 minutes $=1$ hour 30 minutes $=\frac{3}{2}$ hours
$$
10 \times \frac{3}{2}=15 \text { (km) }
$$

Let the sum of the two people's speeds be $x$ km per hour
$$
\begin{array}{c}
\frac{5}{3} x-\frac{3}{2} x=15 \\
\frac{1}{6} x=15 \\
x=15 \times 6 \\
x=90 \\
90 \times \frac{5}{3}=150 \text { (km) }
\end{array}
$$

Answer: The distance between location A and location B is 150 km.
The answer is: 150 .