Question 486593
0.1x + 0.8y= -2.1
0.9x - 0.9y= 5.4 

multiply both equations by 10 to make life easy.
x+8y=-21
9x-9y=54 

1	x	+	8	y	=	-21	.............1				
-9	y	=	54		-9	x	---------2				
/	-9	=									
	y	=	-6	+	1	x					
Substitute y in 		(1)									
1	x	+	8	(	-6	+	1	x	)	=	-21
1	x		-48	+	8	x	=	-21			
1	x	+	8	x	=	-21	48				
9	x	=	27								
/	9										
x=	3										
Plug the value of x in (1)											
1	x	+	8	y	=	-21					
1	*	3	+	8	y	=	-21				
3	+	8	y	=	-21						
8	y	=	-24								
/	8										
y=	-3										
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