Question 1193696
<pre>
                    SPEEDS      TIMES                 DISTANCE

AGAINST WIND         r-10       3869/(r-10)              3869

WITH WIND            r+10       3869/(r+10)              3869

DIFFERENCE                        20
</pre>
With those, you can setup and continue with   {{{3869/(r-10)-3869/(r+10)=20}}}.  Simplify and solve.