Multiply the first equation by 4: $\displaystyle{20}{x}-{8}{y}={112}\usepackage{cmbright}\Huge\$

Add this to $\displaystyle-{20}{x}+{8}{y}=-{100}\usepackage{cmbright}\Huge\$ : $\displaystyle{0}={12}\usepackage{cmbright}\Huge\$

If both equations in the system were true, that would imply that $\displaystyle{0}={12}\usepackage{cmbright}\Huge\$ . Since this is false, you cannot find numbers that make both equations true. In other words, the system does not have a solution.