Question 1042685
The speed upstream is 13-c, where c is the current.
The time it takes is 60/(13-c), as you have with units mi/mi/hr, with units hr.
The time it takes to go downstream is 60/(13+c), and that is 2 hours less than upstream
Therefore, 60/(13-c)-2=60/(13+c)
Your LCD is (13-c)(13+c)
60(13+c)-2(169-c^2)=60(13-c)
780 +60c-338+2c^2=780-60c
780 cancels, 
2c^2+120c-338=0; Notice, this is 120c, not 20c.
divide by 2
c^2+60c-169=0
c=(1/2)(-60+/-sqrt (3600+676) sqrt (4276)=65.39
use positive root (1/2)5.39=2.695 mph
Upstream speed is 10.305 mph
Downstream speed is 15.695 mph
60/10.305=5.822 hours
60/15.695=3.822 hours
{{{graph(200,300,-10,10,-200,100,x^2+60x-169)}}}