Question 468676
speed of boat = xmph
speed of current = y mph

against current --------	3.00	hours					
with current ------	1.50	hours					
								
Distance = same=		12						
Boat speed	=x							
current speed 	=y							
t=d/r								
12	/	(	x	-	y	)=	3.00	
3	(	x	-	y	)	=	12.00	
3	x		-3	y	=	12	....................1	
12	/	(	x	+	y	)=	1.50	
1.50	(	x	+	y	)	=	12	
1.50	x	+	1.50	y	=	12	...............2	
Multiply (1) by 	1.00							
Multiply (2) by	2.00							
we get								
3	x	+	-3	y	=	12		
3	x	+	3	y	=	24		
6	x	=	36					
/	6							
x 	=	6	mph	Boat speed