Question 1064973
x= speed of boat
(x-2) is speed upstream and 24/(x-2) is hours it takes to go 24 miles.
(x+2) is speed downstream, and 24/(x+2) is hours it takes to go 24 miles.
Those two times add to 5 hours
Multiply by (x-2)(x+2) or x^2-4 as common denominator, 
24(x+2)+24(x-2)=5x^2-20
0=5x^2-48x-20
(5x+2)(x-10)=0
x=10 mph in still water.
so 8 mph upstream and takes 3 hours to go 24 miles
and 12 mph downstream and takes 2 hours to go 24 miles.  Total time 5 hours.