9.2. Two cars simultaneously departed from the same point and are driving in the same direction. One car was traveling at a speed of 50 km/h, the other at 40 km/h. Half an hour later, a third car departed from the same point and in the same direction, which overtook the first car one and a half hours later than the second car. Find the speed of the third car.
Answer: 60 km/h.

In half an hour, the first car will travel 25 km, and the second car will travel 20 km. Let $x$ be the speed of the third car. The time it takes for the third car to catch up with the first car is $\frac{25}{x-50}$, and the time to catch up with the second car is $\frac{20}{x-40}$. We get the equation $\frac{25}{x-50}-\frac{20}{x-40}=\frac{3}{2}$, and from it $x=60$.

Comment. Correctly formulated equation or system of equations corresponding to the problem - 2 points.