Read the question and help me, please.

Explanation:

Add the equations by adding the terms straight down.

The x terms add to x+x = 2x.

The y terms add to y+(-y) = y-y = 0y = 0, so the y terms go away

The constants add to 5+7 = 12

The z terms add to -z+z = 0z = 0 and those go away as well

After all that adding, we have 2x = 12 which solves to x = 6 after dividing both sides by 2.