Question 1192234
<pre>
               SPEED             TIME         DISTANCE

UPSTRM           30-c            5/(30-c)         5

DWNSTRM          30+c           10/(30+c)        10
</pre>

{{{1/(30-c)=2/(30+c)}}}

-

{{{2(30-c)=30+c}}}

{{{60-2c=30+c}}}

{{{3c=30}}}

{{{highlight(c=10)}}}