Question 761466
Let r = speed in still water.  You do not know time but you can create expressions for both directions each.


WAY___________rate_____________time____________distance
Up____________r-2______________12/(r-2)_________12
Down__________r+2______________12/(r+2)_________12


Upstream was 3/2 hour MORE than downstream:
{{{highlight(12/(r-2)=12/(r+2)+3/2)}}}


Multiply left and right by the LCD, {{{2(r-2)(r+2)}}} and simplifying,
{{{24(r+2)=24(r-2)+3(r^2-4)}}}
.
{{{48=-48+3r^2-12}}}
{{{96+12=3r^2}}}
{{{3r^2=108}}}
{{{r^2=36}}}
{{{highlight(r=6)}}}