Question 428009
boat speed		x	mph				
current speed 		5	mph				
..							
against current		x	-	5	mph		
with current		x   	+	5	mph		
							
Distance against current		5					
Distance with current		15					
Time = same							
5	/(x-	3	)=	15	/(x+	3	)
5	*(x+	3	)=	15	*(x-	3	)
5	x  	+	15	=	15	x	-45
15	x  	-5	x   	=	45	+	15
10	x  	=	60				
/	10						
	x=	6	mph