Question 760144
{{{x}}} = speed of the current (in mph)
The speed of the boat (in mph) when going downstream is
{{{12+x}}}
The speed of the boat (in mph) when going upstream is
{{{12-x}}}
The time (in hours) that it takes for the boat to go a certain distance is the distance (in miles) divided by the speed (in mph).
From the information given,
{{{24/(12+x)=12/(12-x)}}}
{{{24/(12+x)=12/(12-x)}}} --> {{{24(12-x)=12(12+x)}}} --> {{{288-24x=144+12x)}}} --> {{{288-144=12x+24x)}}} --> {{{144=36x)}}} --> {{{x=144/36)}}} --> {{{highlight(x=4)}}}