If you multiply the third equation by $\displaystyle-{3}\usepackage{cmbright}\Huge\$ and add it to the first equation, the resulting statement is $\displaystyle{0}={0}\usepackage{cmbright}\Huge\$ . You may then have multiplied the third equation by 4 and added it to the second equation, and mistakenly got the resulting statement of $\displaystyle{0}={0}\usepackage{cmbright}\Huge\$ , which would mean that the system has an infinite number of solutions. However when combining the third equation and the second equation in this manner, you should have gotten $\displaystyle{0}={48}\usepackage{cmbright}\Huge\$ , in which case there would be no solution.