Question 1072289
<pre>
                SPEED   TIME       DISTANCE
UPSTREAM        r-3     4/(r-3)       4
DOWNSTR         r+3     10/(r+3)     10
</pre>


Both times are given as the same.
{{{4/(r-3)=10/(r+3)}}}
Solve for r.



-
{{{4(r+3)=10(r-3)}}}
{{{4r+12=10r-30}}}
{{{12+30=6r}}}
{{{6r=42}}}
{{{r=7}}}