Question 1011618
The same question is often asked for help but in different examples.  The solution  to be started here will be generalized and suitable for all examples of this type of problem.


Definition of Variables
r, speed when no wind, calm air
w, speed of wind
{{{d[w]}}}, distance done with the wind
{{{d[a]}}}, distance done against the wind
t, time at which the two distances were found


<pre>
               speed        time        distance
WITH           r+w          t           {{{d[w]}}}
AGAINST        r-w          t           {{{d[a]}}}
</pre>


Variables given values: {{{d[w]}}}, {{{d[a]}}}, r
Unknown variables:  w, t


Using RT=D the basic travel rates rule, the description and data table formed with it gives enough to solve for w and t.


{{{system(d[w]/(r+w)=d[a]/(r-w),(r+w)t=d[w],(r-w)*t=d[a])}}}


The reason that the first equation was formed and included is because it uses only ONE unknown variable, w, which can then be used in either of the next two equations to solve for t.