Because the speed ratio of the two cars is 5: 4, when they meet, A is 5 times to the left, so it is 4 times to the left.

The distance between AB is 9x, and A has to go 4x, so it has to go 5x. Suppose it took an hour to meet.

4x/(5x/a)= 5x- 10/((5x/a)*(6/5))

Explain; The way to go /A's speed = A's way to reach the destination /A * 6/5' s speed.

A can be eliminated after solving.