X+y=12/2=6, x-y=12/3=4, x=5 mile/hour, y=1 mile/hour, so the crew's rowing rate in still water is 5 mile/hour and the rate of current is 1 mile/hour.
A Boat's crew rowed 12 miles downstream in 2 hours. The return trip upstream against the current, covered the same distance, but took 3 hours. Find the Crew's rowing rate in still water and the rate of the current?