Question 874896
Boat speed	speed	x	mph									
current     	speed	5	mph									
..												
against 	current     	x-	5									
with	current     	x+	5									
..												
against	current     	6	hours									
with 	current     	4	hours									
Distance is same.  D=r*t												
6	(	x	-	5	)	=	4	(	x	+	5	)
6	x	-	30			=	4	x	+	20		
6	x	-	4	x	=		30	+	20			
2	x				=		50					
/	2											
x				=		25	mph					
Boat speed	speed	=	25	mph