Question 558830
boat	speed=	x	mph						
current	speed=	y	mph						
with current speed		(x+y) 							
against current speed		(x-y) 							
d=	50	downstream							
50	/	(x+y) 	=	5					
divide by 	5								
10	/	(x+y) 	=	1					
(x+y) 	=	10	............1							
d=18						
18	/(x-y)=	9	against 	wind					
divide by 	9								
2	/(x-y)	=							
x-y=2	.............2		
add up (1) & (2)									
2	x	=	12						
/	2								
x=	6	mph	speed of	boat	in still water				
plug value of x in (1)									
we get 	y= 	4	mph	speed of	current