First equation

2x + 2y -2z =6

Second equation

2x - 2z = 8

If I multiply the second equation by -1 and add the two equations , I get y = -1

Third equation

-1+ z = -2 , then z = -1

By replacing the values of y and z in the first equation, I get x = 3

Fourth equation

3 -1 + 1 = 3

the answer is 3