Consider the following system of equations.

$\displaystyle{x}+{y}+{z}={5}\usepackage{cmbright}\Huge\$

$\displaystyle{x}-{y}-{z}=-{1}\usepackage{cmbright}\Huge\$

$\displaystyle-{x}+{y}-{z}={3}\usepackage{cmbright}\Huge\$

Which of the following steps will successfully eliminate the indicated variable?