Distance from a place A to another place B is 200 km. A car takes 3½ hours to go from A to B and 4½ hours to return from B to A. What is the average speed of the car in the whole journey?

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A and B are friends and their age differ by 2 years. A’s father D is twice as old as A and B is twice as old as his sister C. The age of D and C differ by 40 years.