Question 536731
1    	x		-3	y	=	12	.............1				
1	y	=	80		-9	x	---------2				
/	1	=									
	y	=	80		-9	x					
Substitute y in 		(1)									
1    	x		-3	(	80		-9	x	)	=	12
1    	x		-240	+	27	x	=	12			
1    	x	+	27	x	=	12	240				
28	x	=	252								
/	28										
x=	9										
Plug the value of x in (1)											
1    	x		-3	y	=	12					
1    	*	9		-3	y	=	12				
9		-3	y	=	12						
-3	y	=	3								
/	-3										
y=	-1										
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