If you solve a system and end up with the equations $\displaystyle{x}={0}\usepackage{cmbright}\Huge\$ and $\displaystyle{y}={12}\usepackage{cmbright}\Huge\$ , then the solution is $\displaystyle{\left({0},{12}\right)}\usepackage{cmbright}\Huge\$ . Here, if you multiply the first equation by 4 and add it to the second equation, you will end up with the equation $\displaystyle{0}={12}\usepackage{cmbright}\Huge\$ , which means something very different. The correct answer is: There is no solution.