Question 1141775
r, unknown speed of boat without current
C=12, speed of current
T=4, total trip time
D=36, distance traveled in each direction

<pre>
                SPEED        TIMES            DISTANCE

DOWNSTREAM        r+C         D/(r+C)             D

UPSTREAM         r-C          D/(r-C)            D

TOTALS                       T
</pre>
{{{D/(r+C)+D/(r-C)=T}}}
Solve for r, and then substitute the given values.


Algebra steps may lead to:  {{{r^2-(2D/T)r-C^2=0}}}


If substitute the given values here, then {{{r^2-18r-144=0}}}.
You may find this factorable as {{{(r-24)(r+6)=0}}}.

{{{highlight(r=24)}}}