If you had a system that led to an impossible equation, such as $\displaystyle{0}={1}\usepackage{cmbright}\Huge\$ , then there would be no solution. If you substitute $\displaystyle{1}-{5}{x}\usepackage{cmbright}\Huge\$ for y in the first equation and then simplify, you will end up with the equation $\displaystyle{10}{x}={10}{x}\usepackage{cmbright}\Huge\$ . This equation is true regardless of the value of x. The correct answer is that there are an infinite number of solutions.