13.274. According to the schedule, the train covers a 120 km section at a constant speed. Yesterday, the train covered half of the section at this speed and was forced to stop for 5 minutes. To arrive on time at the final point of the section, the driver had to increase the train's speed by 10 km/h on the second half of the section. Today, the train was again stopped at the midpoint of the same section, but the delay lasted 9 minutes. At what speed did the driver operate the train today on the second half of the section, if the train again arrived at the final point of the section on schedule?
## Solution.

Let $x$ km/h be the original speed of the train. Considering the stop, it will take $\frac{1}{12}+\frac{60}{x+10}$ to travel the second half of the section, from which $x=80$ km/h.

Let $v$ km/h be the speed of the train today. Then $\frac{60}{80}=0.15+\frac{60}{v}$, from which $v=100$ km/h.

Answer: 100 km/h.