Question 693405
Speed is distance divided by time. 

Going upstream slows you down by the speed of the river

{{{v[barge]-v[river]=(24miles)/(3hours)=8mph}}}

Going downstream you go faster:

{{{v[barge]+v[river]=(24miles)/(2hours)=12mph}}}

If you add the two equations, {{{v[river]}}} cancels and you get:

{{{2v[barge]=20mph}}}

{{{v[barge]=10mph}}}