Question 1093565
You might want to arrange the data from the description as a table.
c, speed of the current
t, the equal time both directions taken


<pre>
                       SPEED       TIME      DISTANCE

WITH CURRENT          26+c         t         100

AGAINST CURRENT       26-c         t          80
</pre>


WITH CURRENT will give {{{t=(26-c)/100}}} and AGAINST will give {{{t=(26-c)/80}}}.  Both expressions of t are equal:


{{{highlight_green((26+c)/100=(26-c)/80)}}}-------solve this for c.


{{{20(26+c)/100=20(26-c)/80}}}


{{{(26+c)/5=(26-c)/4}}}


{{{4(26+c)=5(26-c)}}}


{{{104+4c=130-5c}}}


{{{9c=26}}}


{{{c=26/9}}}


{{{highlight(c=2&8/9)}}}{{{mph}}}