Question 1002733
<pre>
            rate          time      distance
UPST        10-5=5        t+4         d
DOWN        10+5=15        t          d
</pre>

RT=D basic uniform travel rates rule


{{{5(t+4)=15t}}} because distance is d both directions.
{{{5t+20=15t}}}
{{{20=10t}}}
{{{highlight(t=2)}}}


Going upstream, 2 hours
Going downstream, 6 hours


You can find d.