Question 316631
let speed of current be x mph

..
speed downstream = 12 mph
speed in still water = 12-x
speed upstream = 12-2x
..
time taken down stream = 1 hour
time taken upstream = 3 hours
..
distance = speed * time
distance upstream + distance down stream = total distance
..
12+3(12-2x)=24
12+36-6x=24
12+36-24=6x
24=6x
x=4 mph