Question 187631
1. y=-4x+3
5y+10x=20 
Since y is isolated in the 1st eqn, sub it into the 2nd one.
5*(-4x+3)+10x = 20
-20x+15 + 10x = 20
-10x = 5
x = -1/2
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y = -4*(-1/2) + 3
y = 5
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2. y=2x+7
5y+10x=20 
Same as above
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3. 6y-x=-12
1/6x+y=3 


4. x+y=6
4y-4x=12  --> x-y = -3
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x+y = 6
x-y = -3
-----------  Add the 2 eqns
2x = 3
x = 3/2
---------
y = 9/2
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5. y=-x+8
x-y=-1 


6. 6x+y=-4
6x-y=-1 


7. y=-x+8
x-y=-1 
The others are similar.  email me via the thank you note if you need help, or I can check your work.