Question 921813
r, rowing speed if no current
RT=D is uniform rates travel rule.
Using multiplicative inverse of R,  T=D/R.


_______________________rate__________time___________distance
UPSTREAM_______________r-2___________{{{13/(r-2)}}}___________13
DOWNSTRM_______________r+2___________{{{13/(r+2)}}}__________13



The description indicates that {{{highlight(13/(r-2)-13/(r+2)=2)}}}.