What you have to do here is get all values in
terms of x.
Start out by changing y – x = 5 to y = 5 + x
Then plug in 5 + x for y in 2y + z = 11
Now you have: 2 (5 + x) + z = 11
10
+ 2x + z = 11
2x
+ z = 1
z
= 1 – 2x
Now you can add x, y, and z or
x + 5 + x + 1 – 2x
The x’s cancel out and you are left with 6 (B).