Question 730127
Boat speed	speed	=x	mph					
current     	speed	=y	mph					
against 	current     	1.5	hours					
with 	current     	  2/ 3	hours					
								
Distance with	current     	12	miles		distance against	current     	12	
t=d/r	against	current     	(x-y)					
12.00	/	(	x	-	y	)=	1.50	
								
1.50	x	-	-1.50	y	=	12.00	....................1	
with	current     	(x+y)						
12.00	/	(	x	+	y	)=	 2/3	
 2/3	(	x	+	y	)	=	12.00	
 2/3	x	+	 2/3	y	=	12.00	
2x+2y=36
x+y=18........................(2)

multiply equation (1) by 2
we get3x-3y=24
multiply equation (2) by 3
3x+3y=54

add up the equations
6x=78
x=13 km/h the speed of boat in stll water
plug x in the equation x+y=18
y=5km/h the current speed