You may have thought that a system of equations should have one solution. However, when attempting to eliminate variables, you should get the statement $\displaystyle{0}={0}\usepackage{cmbright}\Huge\$ from combining the first and third equations. You should get the statement $\displaystyle{0}={48}\usepackage{cmbright}\Huge\$ when combining the second and third equations. If there were one solution you would not get an equation without any variables.