Substitute $\displaystyle{2}{x}-{1}\usepackage{cmbright}\Huge\$ for y in the first equation: $\displaystyle{10}{x}={5}{\left({2}{x}-{1}\right)}+{5}\usepackage{cmbright}\Huge\$

Simplify: $\displaystyle{10}{x}={10}{x}-{5}+{5}\usepackage{cmbright}\Huge\$ or $\displaystyle{10}{x}={10}{x}\usepackage{cmbright}\Huge\$

Since this equation is true no matter what value x is, this means that every value of x will give you a solution. So there are an infinite number of solutions.