Question 1191070
<pre>
                   SPEEDS      TIMES       DISTANCES

downstream         9+3=12       x            12x

upstream           9-3=6        4-x           6(4-x)

TOTAL                             4
</pre>
The distances both directions are equal.


{{{12x=6(4-x)}}}

{{{2x=4-x}}}

{{{3x=4}}}

{{{cross(x=3/4)}}}
{{{x=4/3}}}


She can go {{{cross(12(3/4)=highlight(9))}}}{{{12(4/3)=4*4=highlight(16)}}} miles down the river.