Multiply the second equation by $\displaystyle-{3}\usepackage{cmbright}\Huge\$ and add it to the first equation. The resulting equation is $\displaystyle{0}={0}\usepackage{cmbright}\Huge\$ . This indicates the potential for an infinite number of solutions. You need to check the remaining equation. If you multiply the second equation by 2 and add it to the third equation, the resulting statement is also $\displaystyle{0}={0}\usepackage{cmbright}\Huge\$ . This means all the points are on one plane, so there are an infinite number of solutions.