Answer:
Time : (1.5+ 2.5) = 4 hours before car A
Now in 4 hours car A drives (20 X 4) = 80 km.
car B is ahead 80 km and is increasing faster than car A by 10 km/hour.
That means car B has taken 8 hour to go from A to B.
Therefore, distance between A and B is (8 X 30) = 240 km.