Question 491115
7	x	+	4	y	=	-1	.............1				
1	y	=	20	+	5	x	---------2				
/	1	=									
	y	=	20	+	5	x					
Substitute y in 		(1)									
7	x	+	4	(	20	+	5	x	)	=	-1
7	x	+	80	+	20	x	=	-1			
7	x	+	20	x	=	-1	-80				
27	x	=	-81								
/	27										
x=	-3										
Plug the value of x in (1)											
7	x	+	4	y	=	-1					
7	*	-3	+	4	y	=	-1				
-21	+	4	y	=	-1						
4	y	=	20								
/	4										
y=	5										
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