13.104. The length of the bus route is 16 km. During peak hours, the bus switches to express mode, i.e., it significantly reduces the number of stops, as a result of which the travel time from the beginning to the end of the route is reduced by 4 minutes, and the average speed of the bus increases by 8 km/h. At what speed does the bus travel in express mode?
Solution.

Let $x$ km/h be the speed of the bus in express mode. Then the travel time in this mode will be $\left(\frac{16}{x-8}-\frac{1}{15}\right)$ hours. According to the condition, $\left(\frac{16}{x-8}-\frac{1}{15}\right) x=16$, from which $x=48$ km/h.

Answer: 48 km/h.