<human>:  Karen is paddling her canoe up a river against the current. On a still pond, Karen can paddle 10 miles per hour. The river flows in the opposite direction at 4 miles per hour. If the river is 12 miles long, how many hours will it take Karen to paddle up it?
<bot>: How fast is Karen paddling? ** First find Karen's net speed by subtracting the speed of the current: 10 mph - 4 mph = <<10-4=6>>6 mph
How many hours will it take Karen to paddle up the river? ** Then divide the length of the river by Karen's speed to find how long it takes her to paddle up it: 12 miles / 6 mph = <<12/6=2>>2 hours
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