Question 1090552
<font color="black" face="times" size="3">Start with the first equation 4x+y=8. 


Isolate y. In other words, get y all by itself on its own side. We do this by subtracting 4x from both sides


4x+y=8


4x+y-4x=8-4x


y=8-4x


y=-4x+8


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The equation y=-4x+8 basically says that y is the same as -4x+8. Because of this, we can replace every 'y' in the second equation with '-4x+8'


6x-9y=12


6x-9( y )=12


6x-9( <font color=blue>y</font> )=12


6x-9( <font color=blue>-4x+8</font> )=12 ... note how the terms in blue indicate how the replacement is happening


So the answer is choice D


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