You probably substituted correctly into Equation B, but then made a mistake solving for y. If you check your answer by substituting into Equation B, you get $\displaystyle{4}{\left({2}\right)}+{3}{\left({11}\frac{{1}}{{3}}\right)}={26}\usepackage{cmbright}\Huge\$ or $\displaystyle{8}+{34}={26}\usepackage{cmbright}\Huge\$ , which is false.