Question 549707
Boat  	speed	=x	mph					
current     	speed	=y	mph					
against current , x-y		12	hours					
with current , x+y		3	hours					
								
Distance = same=		72	miles					
t=d/r	against	current     						
72	/	(	x	-	y	)=	12.00	
12	(	x	-	y	)	=	3.00	
	With	current     						
12	x		-12	y	=	72	....................1	
72	/	(	x	+	y	)=	3.00	
3.00	(	x	+	y	)	=	72	
3.00	x	+	3	y	=	72	...............2	
Multiply (1) by 	1.00							
Multiply (2) by	4.00							
we get								
12	x	+	-12	y	=	72		
12	x	+	12	y	=	288		
24	x	=	360					
/	24							
x 	=	15	mph					
								
plug value of x in (1)								
12	x		-12	y	=	72		
180			-12	y	=	72		
-12	y	=	72	-180				
-12	y	=	-108					
	y	=	9	mph				
	Boat  	15	mph					
	current     	9	mph					
								
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