Question

solve my substitution (medal and fan)

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

Answer 1

2x + 2z = 4
2x = -2z + 4
x = -z + 2

-x - y - z = -8
-(-z + 2) - y - z = -8
z - 2 - y - z = -8
-2 - y = -8
-y = -8 + 2
-y = -6
y = 6

-4x + 4y + 5z = 7
-4(-z + 2) + 4(6) + 5z = 7
4z - 8 + 24 + 5z = 7
9z + 16 = 7
9z = 7 - 16
9z = - 9
z = -1

x = -z + 2
x = -(-1) + 2
x = 1 + 2
x = 3

lets check it now...
-x - y - z = -8
-3 - 6 -(-1) = -8
-9 + 1 = -8
-8 = -8 (correct)

check..
-4x + 4y + 5z = 7
-4(3) + 4(6) + 5(-1) = 7
-12 + 24 - 5 = 7
- 17 + 24 = 7
7 = 7 (correct)

your answer is : x = 3, y = 6, and z = -1 or (3,6,-1)