Math (Reiny please help!)

Solve the system by substitution.

-x-y-z=-8
-4x+4y+5z=7
2x+2z=4

I am very confused about this. Can someone please explain how to do this?

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  1. The actual steps will vary from person to person, and there is no single way to solve this.
    You sort of have to decide on the simplest equation as a starting point.
    In this case it is the last equation, it only has two variables.
    2x + 2z = 4 , or
    x + z = 2 ---> x = 2-z
    I will now sub that into the 1st and the 2nd

    -x-y-z=-8 ----> x + y + z = 8
    2-z + y + z = 8
    y = 6 ----> well that was lucky

    in the 2nd:
    -4x + 4y + 5z = 7
    -4(2-z) + 24 + 5z = 7
    -8 + 4z + 24 + 5z = 7
    9z = -9
    z = -1
    then x = 2-z = 2+1 = 3

    x = 3
    y = 6
    z = -1

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  2. THANK YOU!!!!!!!!!!

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  3. you are welcome

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