Question 1191070
.



            The solution by @josgarithmetic is  INCORRECT,  giving incorrect answer of  9  miles.


            I came to bring a correct solution.




<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}}}

{{{x=4/3}}}


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