Add the first and second equations to get $\displaystyle{y}+{z}={10}\usepackage{cmbright}\Huge\$ . Add the second and third equations to get $\displaystyle{5}{y}+{5}{z}={8}\usepackage{cmbright}\Huge\$ . If you multiply the first new equation by $\displaystyle-{5}\usepackage{cmbright}\Huge\$ and add it to the second new equation, you get the equation $\displaystyle{0}=-{42}\usepackage{cmbright}\Huge\$ . Because this is a false statement, there is no solution to this system of equations.