Question 920761
r, speed if no wind
w, speed of the wind


____________________speed__________time_________distance
AGAINST_____________r-w____________2&1/2________{{{d=(r-w)(2&1/2)=600}}}
WITH________________r+w____________1&2/3________{{{d=(r+w)(1&2/3)=600}}}


Two linear equation in the two unknown variables r and w.


AGAINST:
{{{(r-w)(5/2)=600}}}
{{{5(r-w)=1200}}}
{{{r-w=12*20}}}
{{{highlight_green(r-w=240)}}}


WITH:
{{{(r+w)(5/3)=600}}}
{{{5(r+w)=1800}}}
{{{r+w=18*20}}}
{{{highlight_green(r+w=360)}}}


Elimination Method would be easiest to use.