Question 442300
against current x-		70.00	hours						
with current x+		10.00	hours						
									
Distance = same=210							
Boat speed	=x								
current speed 	=y								
t=d/r									
210/(x-y)=70.00		
70(x-y)=210.00		
70x-70y	=210	....................1		
210/(x+y)=10.00		
10.00(x	+y)=210		
10.00x+10.00y=210	...............2		
Multiply (1) by 	1.00								
Multiply (2) by	7.00								
we get									
70x-70y=210			
70x+70y=1470			
140x=1680						
/140								
x =12	mph	Boat speed					
plug value of x in (1)									
70x-70y=210			
840-70y=210			
-70y=210-840					
-70y=-630						
y=9	mph	current speed