Multiply the second equation by $\displaystyle-{6}\usepackage{cmbright}\Huge\$ : $\displaystyle-{30}{x}+{42}{y}={6}\usepackage{cmbright}\Huge\$

Add this to $\displaystyle{30}{x}-{42}{y}=-{6}\usepackage{cmbright}\Huge\$ : $\displaystyle{0}={0}\usepackage{cmbright}\Huge\$

Since this is true regardless of the value of x or y, there are an infinite number of solutions.