Question 480771
boat  	speed	=x	mph					
current  	speed	=y	mph					
against current x-y		70.00	hours					
with current x+y		10.00	hours					
								
Distance = same=		210	miles					
								
								
t=d/r								
210	/	(	x	-	y	)=	70.00	
70	(	x	-	y	)	=	210.00	
70	x		-70	y	=	210	....................1	
210	/	(	x	+	y	)=	10.00	
10.00	(	x	+	y	)	=	210	
10.00	x	+	10.00	y	=	210	...............2	
Multiply (1) by 	1.00							
Multiply (2) by	7.00							
we get								
70	x	+	-70	y	=	210		
70	x	+	70	y	=	1470		
140	x	=	1680					
/	140							
x 	=	12	mph					
								
plug value of x in (1)								
70	x		-70	y	=	210		
840			-70	y	=	210		
-70	y	=	210	-840				
-70	y	=	-630					
	y	=	9	mph