Solve for z a=x+y+z

$a = x + y + z$

Rewrite the equation as $x + y + z = a$ .

$x + y + z = a$

Move all terms not containing $z$ to the right side of the equation.

Subtract $x$ from both sides of the equation.

$y + z = a - x$

Subtract $y$ from both sides of the equation.

$z = a - x - y$