Suppose the speed of car B is 7X, then the speed of car A is 8X, and the distance ratio when AB meets is 8: 7.

After meeting, the speed ratio of AB is 8X:(7X+ 15), and the distance ratio of AB is 7:8. Because they arrived at the same time, therefore:

8X/(7X+ 15)=7/8。 7(7X+ 15)=8*8X， 15X= 105，X=7

Then the speed of the car is a = 8x = 7x8 = 56km/h. ..