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9. Solve the system by substitution.

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

Eq3: 2x + 2z = 4.

Z = 2-x.

In Eq1 replace z with 2-x.
-x -y - (2-x) = -8
-x - y -2 + x = -8
Y = 6.

In Eq2, replace y with 6 and solve for z:
-4 + 4*6 + 5z = 7.
Z = -13/5.

Z = 2-x.
-13/5 = 2-x
X = 2 + 13/5 = 23/5.
(x,y,z) = (23/5, 6, -13/5).

To solve the system of equations by substitution, follow these steps:

1. Begin by isolating one variable in one of the equations. Let's start by isolating one variable in the first equation. We can choose either x, y, or z.

Let's isolate x in the third equation:
2x + 2z = 4

Start by subtracting 2z from both sides:
2x = 4 - 2z

Then divide both sides by 2 to solve for x:
x = (4 - 2z) / 2
x = 2 - z

2. Now that we have x in terms of z, substitute this expression into the other two equations.

Substitute x = 2 - z into the first equation:
-x - y - z = -8
-(2 - z) - y - z = -8
-2 + z - y - z = -8
-z - y - 2 = -8
-z - y = -8 + 2
-z - y = -6
z + y = 6 (Equation 1)

Substitute x = 2 - z into the second equation:
-4 + 4y + 5z = 7
-4 + 4y + 5z = 7
4y + 5z = 7 + 4
4y + 5z = 11 (Equation 2)

3. Now, you have a system of two equations in two variables: z and y (Equations 1 and 2). Solve this system to find the values of z and y.

Multiply Equation 1 by 4 and Equation 2 by -1 to eliminate y:
4z + 4y = 24 (Equation 1)
-4y - 5z = -11 (Equation 2)

Add the two equations together:
4z + 4y + (-4y) + (-5z) = 24 + (-11)
4z - 5z = 24 - 11
-z = 13

Divide both sides by -1 to solve for z:
z = -13

Substitute z = -13 back into Equation 1 to solve for y:
(-13) + y = 6
y = 6 + 13
y = 19

4. Lastly, substitute z = -13 and y = 19 into any of the three original equations to solve for x.

Let's substitute into the third equation:
2x + 2z = 4
2x + 2(-13) = 4
2x - 26 = 4
2x = 4 + 26
2x = 30
x = 30/2
x = 15

Therefore, the solution to the system of equations is x = 15, y = 19, and z = -13.