Question 915070
r, salmon rate when no stream current
c, stream current speed


_________________rate_________time_________distance______equation
downstream_______r+c__________12___________200___________{{{(r+c)*12=200}}}
upstream_________r-c__________15___________200___________{{{(r-c)*15=200}}}


Two linear equation in the two unknown variables, r and c.