Car A goes from Ha Noi to Da Nang. Car B go from Da Nang to Ha Noi. The ratio of the speed of car A and car B is 5:4. After 2 cars meet, Car A decrease its speed by 1/5 of its speed, car B increase its speed by 1/5 of its speed. When car A reached Da Nang, car B is 25 km from Ha Noi. What is the distance between Ha Noi and Da Nang?
