The speed of a boat in still water is 6 km/h. Time taken by the boat to cover a certain distance upstream is 3 hours more than the time taken to cover the same distance downstream. If the speed of the stream is 2 km/h, then what is the total distance (upstream and downstream) covered by the boat?

• A. 24 km
• B. 18 km
• C. 36 km
• D. 48 km