.
Let D be the distance between the cities A and B.
Till the moment of the meeting the car A covered the distance (D + 30) km,
while the truck covered the distance of (D - 30) km.
Car A spent hours to cover the distance (D+30) at the rate 50 km/h.
Truck B spent hours to cover the distance (D-30) at the rate 40 km/h.
The time spent is the same, which gives you an equation
= .
To solve it, cross multiply and simplify:
40*(D+30) = 50*(D-30) ====>
40D + 1200 = 50D - 1500 ====> 1200 + 1500 = 50D - 40D ====> 10D = 2700 ====> D = = 270.
Answer. The distance between the cities A and B is 270 kilometers.
Check. = 6 = . ! Correct !