Question 1077432
<pre>
                 SPEED    TIME             DISTANCE
AGAINST WIND      r-6     3933/(r-6)       3933
WITH WIND         r+6     3933/(r+6)        3933
Difference?                 12
</pre>

Time against the wind took longer, so was larger.
{{{3933/(r-6)-3933/(r+6)=12}}}
Solve this for r.