Let 'x' and 'y' be the speed (in km/hr ) of cars starting from both A and B respectively. If they both move in east direction, then B will overtake A only if y>x Also, relative speed of both the cars when they move in east direction =(y−x)km/hr It is mentioned that they take 7 hours to meet. i.e. they travel 350km in 7 hours with a relative speed of (y−x)km/hr Hence, (y−x)=350/7=50km/hr