Question 724440
x+y+z=45
6x+5.40y+4.5z=252
z=2y

substitute z

x+y+2y=45
x+3y=45
6x+5.4y+9y=252
6x+14.4y=252

1.00	x	+	3.00	y	=	45.00	.............1	
Total value								
6.00	x	+	14.40	y	=	252.00	.............2	
Eliminate	y							
multiply (1)by		14.40						
Multiply (2) by		-3.00						
14.40	x		43.20	y	=	648.00		
-18.00	x		-43.20	y	=	-756.00		
Add the two equations								
-3.60	x				=	-108.00		
/	-3.60							
x	=	30.00						
plug value of			x	in (1)				
1.00	x	+	3.00	y	=	45.00		
30.00		+	3.00	y	=	45.00		
			3.00	y	=	45.00		-30.00
			3.00	y	=	15.00		
				y	=	5.00		

z=2y
z=10