Question 416168
let speed in still water =x mph			
current speed 	4 mph			
					
upstream speed = x-4					
downstream speed = x+4					
					
Distance= 60 miles			
					
Time upstream + time downstream = 5 hours	
t=d/r					
60/(x+4)+60(x-4)=5				
LCD =(x	-4)(x+4)								
60*(x-4)+60(x+4)=5				
60x-240	+60x+240=5(X^2-16)
120x=5X^2-80								
5X^2-120x-80
a= 5, b= -120, c=-80
b^2-4ac= 12800
{{{x1=(120+sqrt(12800))/(10)}}}
x1=23.3 mph

{{{x2=(120-sqrt(12800))/(10)}}}
=0.69 -- not practical